I used a modified version of what they call the "Extinction" method. It's similar to some of what GiJose said about the checking at intervals that gradually increase. As he mentioned, babies of ~6 months are capable of sleeping through the night without needing to eat, so that's considered the time you can give it a go. You check that they're freshly changed, fed before bed (we used to do it right before bed), comfortable, etc. You do whatever mini-routine you do for your bedtime (we did a sound app on, a little bit of rocking, and then into the cot), and then leave. When they fuss or cry, wait a few minutes first, then go in and gently pat or lay your hand on their back or chest for reassurance, but don't pick up or talk. Just pat a little, or wait for a few moments, then leave. If they fuss or cry, wait for a slightly longer interval. Rinse repeat. I did this, and the longest interval I got to was not quite 30 mins on the first day, less than 20 mins the next day, and on the third day I only had to go in once (at the 7min? mark). After that she was pretty much 7-7. Before this I'd been getting maybe one 2hr stretch of sleep at best and she'd wake 4-6x a night. It was hell. She's been fantastic ever since (she's almost 4 now), and there have been no behavioral issues or concerns. She's a lovely kid and the full night of sleep has had a good effect on her as well. We have to remember that it's not just us getting crummy sleep but them too. Anyway, if you want more details, I'm happy to share via PM if you like. There are things you can do to pave the way before you try it like we did.
It was the weight tracking that revealed it. I breastfed both kids, and my first kid had pretty 'loose' poop, so when baby #2 had it I didn't think anything of it. That's just what breastfed poop looked like in my mind. She also didn't fuss at the boob or seem bothered by eating. She just slept horrifically (also like my first). After the 3rd weigh-in, though, it started to show that she wasn't gaining almost anything. She went from 50th percentile at her first weigh-in (even gained after being born!) down to between the 2nd and 9th, and no matter what I did to feed more or increase production or even supplement, she barely put on anything. They couldn't test her for a dairy allergy at that age, but they suggested it might be it and put me on a no-dairy diet (hell) and then Neocate, a super hypoallergenic formula. Eventually I had to stop breastfeeding completely at 4-ish months and just use the formula. She gained finally and stopped doing a nosedive in the weight department. She also started sleeping through the night on her own at 7 months. They said that the cramps/irritation/gas from the dairy allergy was most likely the thing that woke her so much, and she would comfort feed for the pain, but that would just bring more irritation because of the allergy... -_- I felt so horrible. Everything's sorted now, but her poop is horrendous if she has anything with concentrated dairy in it still. Never seemed fussed aside from that, though. Have you guys had any weight gain issues?God, fuck. This is bleak. We're losing our damned minds.
Less bleak, but our baby is colicky, so... :/
How could you tell your child had a dairy allergy? We had suspected ours did, but some of the "symptoms" we realized were probably just colic, as switching to a soy formula (+breast milk) didn't seem to affect anything. I'd kill for our daughter to be on a similar sleep schedule. She had a decent run where she was sleeping 4-5 hours a stretch before getting restless and constantly waking up, but now she literally lasts about 20 minutes before her eyes just pop open. It's awful.