T., it sounds like you have a LOT on your plate! With babies close together like that (1 y, 2 y, and a 3 yr old) it's almost like triplets. They're all still babies with a lot of needs, so that can be really really intense.
That 1 yr mark is ripe time for a lot of different things to happen, as you probably already know since you've been through this 3 times before:
* teething pain or other physical growing pains
* wanting to be mobile or already mobile, but not quite there yet (crawling/cruising/walking/running)
* frustrations with wanting to communicate, but not being able to talk/say much/say it clearly, so crying is more common
* separation anxiety is also commmon around this age
* possible increase in variety of foods eaten, so possibility of new food sensitivities (typical problems are dairy, wheat, eggs, nuts, etc.) making her feel yucky, thus more crying
So, a few things to try:
1) Teething pain - I know it seems obvious, but there are so many times where I've tried to figure out what's bothering my babies, and it boils down to unrecognized teetehing. Once we figure that out, we can offer stuff to help w/ the pain like cold, damp washcloth to chew on, other teethers that are hard or nubby, those hard biscuits just for babies, teething gel, and worse case scenario like if there's too much pain keeping them up all night, infant motrin.
2) Wanting to be mobile - well, this will work itself out, but you can certainly give them lots of floor time to crawl, climb, cruise, walk safely.
3) Frustration due to wanting to communicate --> Start using sign language every day to cut down on the frustration/crying related to wanting to communicate but not yet being able to say/speak much or clearly. Signing would benefit your 1, 2, & 3 yr olds, and your 6 yr old would likely catch on super fast and be a wonderful teacher to the younger sibs. A wonderful, fantastic DVD series for teaching useful signs to toddlers is "Signing Time" - you can watch these on your public television station like KET in the Cincinnati area (http://www.signingtime.com/pressroom/stationcarriage.htm), get them from your local library, or buy them online (eBay has some decent prices for the package - well worth the $$$, since it's like getting a full toddler sign language course that you can watch over and over again for you & your kids). Our whole family absolutely adore this DVD sign language series - used it (still are, actually) with both of our kids and it's so cool that our 12-month-old son doesn't have to get frustrated when he wants to eat or drink (from the videos, we've learned signs for eat, banana, water, cracker, more, hurt, book, bird, horse, boat, doll - there are MANY, many more than that, and we're still learning). He just signs to us. It's a real relief, for me as a parent AND for him as a baby really wanting to communicate! For more information on this series, check out...
Signing Time website (free clips there to check out):
http://signingtime.com/
At the Cincinnati Library:
http://catalog.cincinnatilibrary.org/uhtbin/cgisirsi/8Dr3....
On eBay:
http://cgi.ebay.com/SIGNING-TIME-BABY-SIGN-LANGUAGE-VIDEO...
A free, online video dictionary of signs is also available here (a *wonderful* resource!):
http://commtechlab.msu.edu/sites/aslweb/browser.htm
4) Separation anxiety - when she's particularly clingy, screaming, fussy, carry her around with you on her back using a good baby carrier like the Ergo carrier which is comfortable for you and baby, can be worn on front or back or side, will last through until your baby is a preschooler - 3 of the best options are:
The Ergo Carrier
The Beco Carrier
The Sutemi Carrier
More info on these carriers (including video clips of the many easy, convenient ways to use them!) available at:
http://www.theportablebaby.com
http://www.sobebabies.com
http://www.peppermint.com
http://www.ecobabies.com/
Plus, there's a local group of moms here in Cincinnati that meet once a month to share/try out/learn about how to carry your baby comfortably. Here's info on the group, the next meeting, etc.:
FEB 3, 2007 - 1:00 - 3:00 p.m.
http://groups.yahoo.com/group/cincinnatiNINO/
5) Food sensitivities - know how to recognize the signs:
http://kellymom.com/nutrition/solids/first-foods.html#all...
http://www.askdrsears.com/html/4/T041800.asp#T041803
Sometimes the only way to figure out if your child is sensitive to something is to completely remove that food from their diet for 2-4 weeks and then reintroduce it. Mild allergy symptoms can be masked, though the child can still be experiencing discomfort, and eliminating the food allows their system to heal. Then reintroducing the food will give a more accurate picture of whether your child is indeed sensitive or even allergic to the food.
And last, but certainly not least, when you say "but im gettin so stressed lately and feel like im yellin at everyone all the time because of the screaming and crying nonstop for no reason" -- I just wanted to say I really feel for you! If at all possible, try to take a little time to yourself to recharge your batteries, and that might be a 20 minute walk by yourself without screaming (yes, even out in the cold), or a nice shower without the kids, or grabbing a cup of tea with a good friend for some kid-free, adult conversation. A little recharging can really help us weather the intense and important needs of our babies (yes, even through all the screaming & toddler frustration!).
Hope some of this is helpful to you. Best of luck!