Sleep begets sleep.
Odd, isn't it? For the first 5 years of his life the later we put our son to bed, the earlier he got up. It seems to be near universal, the same has been true with every other mum I've met.
I think the other mums are dead on with moving bedtime earlier. Just make sure to try changing him & feeding him right before you go to bed. That way he won't wake up wet and hungry...because you've already woken him up and taken care of that. If YOU are the one waking him up, you stand a better chance of keeping him drowsy, since the lights will be off...he'll be warm...and then full of warm milk and a dry diaper...and then back off to dreamland. If he's teething put a little ibuprofen in his bottle, and if you use it, oragel/numgum on before you put him back down.
Other things to try:
- Consistant noise ... like music playing gently in the background.
- Consistent light ... doesn't actually exist. Young children are especially sensitive to light. WE know it's only 5 o'clock, but to them it's dark out. or conversely, WE know it's only oh-dark-thirty, but to them it's dawn. We found we had the best luck with sleep consistency when we changed the bedtime routines to coincide with sunrise sunset. Pretty much and hour later in the winter, and an hour before in the summer. So our son got a LOT of sleep in the winter and less in the summer...pretty much until he learned to tell time. It's a pretty natural thing to do. Rise and fall with the sun.
So too, these little reversions are common, especially in times of stress...like illnesses and teething. He may just be needing a little extra snuggle time.
If you have a supportive spouse you could try two on, two off, with trading getting up in the middle of the night. Pretty much ANYONE can handle losing a little sleep a couple nights a week. Nearly NOONE can handle losing sleep everynight...and one day on one day off doesn't really give anyone's body time to recoup...it's just endless OMG it's my night again.
Of course, my hubby never got up in the night, ever. Well twice. I learned the two on, two off trick from a friend who came to stay with us for a month. If yours won't give you a break either, try hiring a babysitter so you can get a nap in in the afternoon.
Good luck.
This too, shall pass. Not as quickly as you'd like, probably, but it will get back to "normal" soon.