Mighty Fits at Bed Time

First of all 6 months olds do not throw temper tantrums... that will not happen until he is at least one.
Since this is a new thing and he is crying so violently I would suggest that something is bothering him and you need to find out what it is. If you are feeding him solids at night it could cause him discomfort when laying down (ever ate a big meal right before bed?). He could be teething, he could have an ear infection or another physical issue.
I would get to the bottom of this and not let him scream until hyperventilation/vomiting.
Good luck.

He may still be hungry. Try giving him a bit more breast milk or formula
(whever you are giving him).
His only way to tell you that something is wrong is to cry or throw this fit.
Did his ped say it was ok (age approp) to give him the oatmeal.
He may have a hurt belly.
He may need to be burped.
Could still be hungry (more breastmilk or formula)
He may need to be held more instead of being put right down.
Could be any one of these things or a compilation.
I don't know that he will be ready for bed when you are when you go back to work. I know that it is hard to hear but it's true.
He might need to stay up a little bit more before being laid down.
They go through a lot of stages.
Good luck & work "with this instead of against it". You'll find it works better & you will all be less stressed.
Wishing you the best. Hang in there. This will pass soon.

Nurse first.
For the 1st year of life... breastmilk or Formula is a baby's PRIMARY source of nutrition... not solids and not other liquids. And to nurse, on-demand.
ESPECIALLY at growth-spurts. Which, 6 months is a growth-spurt.
ALSO in tandem with this, many babies begin to teethe at this age.
AND, they are also beginning to feel separation anxiety.
SO, MANY things at the SAME time, happening to a baby. Thus, their sleep... gets tweaked.
One of many.... developmental based, phases.
Normal.

Nurse him, primarily.
BEFORE, solids. Because, if you nurse him after solids, a baby will be too full to nurse. They need your breastmilk, primarily. For the 1st year.
My kids, both had GINORMOUS appetites. Breastmilk metabolizes fast. Their tummy is tiny. Feeding solids, does NOT make a baby sleep, nor more, nor better. Nurse him.
Even during wakings at night.

And he may have gas. This causes pain. So this may also be happening. Too. In conjunction with the other things I mentioned.
It is thus, very hard, for a baby to handle.
They need nursings and comfort. And watch what you eat, so that is does not cause gas in him.

Don't make him cry it out.
A baby has no coping ability.
It affects the brain... to be crying so long.
Or they just give up... because their Mommy does not come.

MANY developmental phases, will arise.
Normal.
It just is.
Lack of sleep for them, the baby, too.
And lack of sleep for a baby, makes them more fussy and inconsolable.
But they are too young, to cope or to problem solve, that.
It is growing pains, for the baby.
Which is, physical/cognitive changes in the baby.
And my kids at that age, hit teething AND separation anxiety, already at 6 months old. PLUS they were growing and changing a ton.... cognitively and physically. And even if they were on solids at 6 months... my kids still nursed... every 2-3 hours. ALL day, ALL night. And I woke and nursed them. Even my Hubby, was proud of me. He knew it is hard work. But our kids were growing so well, and were nourished.
And they grew like weeds and was very healthy and developed on par. Even if, sleep at times, were hard. For them. And then, me.

Get the book "What To Expect The First Year" and "What To Expect: The Toddler Years."

Solids... is NOT as nutritionally dense... as breastmilk.
And it does not, "replace" breastmilk or Formula.

Many... late nights are ahead...he is a baby.
Even a 1 or 2 or 3 or 4 or 5 year old does not just go to bed... easily or quietly or on-time, just because the parents have a work schedule and bedtime for themselves.
This is how it is.

I rule out medical first: Ears, sinuses, teeth. Screaming when laid flat (babies are propped up to nurse, in car seats, the vast majority of the time, they're reclined or vertical, not flat) is HUGELY indicative of an ear infection or sinus infection.

Since he's waking up when you lay him down, 1 will get you 10, he's suddenly feeling like someone is stabbing his head with an icepick. That's ears or sinuses... and it's a trip to the Ped (or ER since it's a holiday weekend...now that they don't have OTC meds in this country (that's another rant for another time. Know... kids ALWAYS get sick at 5pm on a Friday... or precisely 1 minute after your Ped closes. It's just how it is. Murphey's Law).

Teeth are another probability. A lot of kids are so active in the daytime they aren't cranky or fussy at all with their teeth cutting (and as an adult who has cut a tooth... that HURTS... like knife in the mouth hurts) UNTIL it's bedtime and everything is quiet. Then they can't sleep because their mouth hurts. I call this one "The Tylenol Test". If a dose of tylenol later they're conked out sleeping like a log... it's a pain issue. And one fixable with tylenol (which ears and sinuses usually aren't).

I rule out medical first, because I learned the hard way. Trying a gazillion things and then HEADSMACK. Oh. This easily fixable thing. Of course, that was back when infant drops were available OTC. Super easy to fix pain and congestion at home, no $100 copays needed. But again. A rant for another time.

If it's not medical ... time to check the other usual suspects.

1st... Still hungry? This is the cluster feeding thing that happens at around 6mo, and again at 9-10mo (and probably was around a lot as a newborn at 1 week, 3 weeks, etc.). Nursing, half hour break, nursing again. It's to kick up your supply, and because they're about to launch into a major growth spurt. The cluster feeding tells your body to start amping up both supply and changes the content of your milk. It's a pain. But it only lasts for a few days to a week or so.

2nd... if you started solids recently (past month), ditch them unless you're under orders for reflux. Nothing but nothing will screw up an infant's sleep faster than adding solids before their digestive system is ready for them. They can't digest them (like eating cardboard) so their systems back up, get gassy, cramp. Only about 50% of infants can digest solids at 6mo. If you're on here awhile you'll see a trend "I just started my infant on solids, and now they're cranky, fussy, can't sleep, constipated, gassy..." the list goes on. The easy fix is this: Stop Solids. Peds say you can go ahead and TRY solids at 6mo. ANY bad effects (sleep, attitude, pain, etc.) one needs to stop. Wait a few months. Most babies like the way things TASTE about 3 months before they can digest them without major upset. Tasting is great... no problemo. Just don't do more than about a teaspoon or table spoon or you'll have problems!!!

3rd Temp (too hot, too cold)

4th (enviornment... lights, sounds, textures)

5th sepearation anxiety. This is THE age to start peek a boo. The realization that they're alone can happen between now and three months from now. Kicks in some major separation anxiety in many infants. So you play peekaboo. You duck around a corner and come back. The whole thing is leave, come back, leave, come back. Build up the trust that you will ALWAYS be back... and then they just dig it and are fine.

I'd lay serious money on it being medical ... but if it's not... keep the others in mind.

A few things to consider.

Teething, you may not even see or feel them but he does. They are very painful. See what your doc recommends for the pain. Freeze some baby wash cloths and let him chew on them.

Ear ache. Is he pulling at his ears at all? If he is, you may need to have his ears checked.

Does he sleep on his tummy yet? Could be this is a more comfortable position than on his back. Can he lift his head on his own and turn it.. That will let you know if he is ready to sleep on his tummy. The weight on his tummy will help him digest the oatmeal and formula.

Could be he is not sleepy. When children are about to go through a big growing spurt, they sometimes have a big change in their sleeping habits.
Make sure when you do this final feeding you keep the room dark, no talking, the least amount of attention towards him.. All of this is stimulation to him. When you change his diaper the final time, again, do this in the darkest room as possible and do not interact with him.

Also how as his schedule today? Did you stay on the same schedule he normally would have had? Or was there a lot of running around doing errands, visiting.. etc.?. Infants and young children thrive on schedules. You mess with it and it messes them up.

I know that we cannot stay on a schedule 24/7, so when we mess with it, we need to be prepared for some meltdowns and struggles.

Hang in there. You have time to figure out what is going on and solve his problem.

Here's the thing. Feeding a baby this young especially late at night will make more issues since he will likely get horrid gas from all the food in his belly when it can't do anything with it since he's too young to have it.

He could be coming down with something, he could be having a growth spurt and need to be fed during the night, at this age they still need to eat about every 3-4 hours. Sleeping all night in pretty rare this young, there is really no telling what may be going on.

He is an infant. When he cries you need to go to him and comfort him. Obviously he will cry until he makes himself sick. You may be tired the next day at work but he needs his mom or dad to take care of him. He will outgrow this in no time but until he does you need to just go get him and rock him or co-sleep with him so you can both get a nights rest.

If you give food other than milk ( nursing ) give it early in the evening and like regular meal times, not at bedtime. One thing to keep in mind is that he's 6 months old now and not 3 mo or so and he will start to change in how he does many things. Maybe you need to rock him or play with him more or sing to him or whatever he likes. You'll discover what he needs and likes by trying different things. I am for crying it out to a point but not to the point of making himself sick. Also one thing you said is a red flag to me. You may be working and not wanting late nights but you have a baby. He comes first and babies are not on a working schedule often times. You will have to go to work tired and work around the bedtime until you get it adjusted because the baby comes first and doesn't understand jobs and work and schedules. As he gets older and older you may have to deal with bedtime in many ways with many issues so you need to prepare yourself for that now. Toddlers don't often 'beg' to go to bed quietly either.

Calms Forte. Buy it and keep it on hand. It stops tooth pain, makes gas go away, is a long standing remedy for babies and toddlers. Is homeopathic and cheap to buy.
I have used it for multitudes of children. It's good for anxiety, pain relief and lots more. A mother without it is operating with her hands tied behind her back.

Maybe you could try co-sleeping if you don't want late nights. Unfortunately babies don't understand work schedules and you will have to work with them until they are old enough to understand, which will be a few years. One thing to remember is that babies are always changing. Don't get too use to how they are doing something because they will all of the sudden start doing something else. Instead of letting him cry it out, you may just want to go him sooner and you may find that he calms down quicker. He does sound like he is in pain, I would take him to the dr.

If it just started there may be a physical problem when laying down. Does he do it at other times when laying down. You may want to see a doctor to see if there is some physical ailment.

N.

Sounds like he wants to stay close to his mama. If you are all going to bed at the same time, just bring him to bed with you. Everyone will sleep better and you won't have to get up for middle of the night feedings! If you were putting him down before you were going to bed, try letting him fall asleep in your lap while nursing. Then just hold him while you read a book, watch TV, surf the web, or grade papers. He's letting you know that he needs you, he may be scared when left alone and will feel better when close to you. Do you wear him at all? He may enjoy a sling, mei Tai, or Ergo which you could wear as you do other things. Or bundle up and go for a walk. Read books about age development, I believe there is a growth spurt at 6mos, body and brain. The Baby Book by Dr Sears is very good.