You'll hear lots of people talking about the 4 month sleep regression. You'll hear lost of people saying their baby didn't come out of the "4 month" sleep regression for several months. You'll hear people saying this will pass in a way that suggests you don't need to do anything different, just wait it out.
I don't agree with any of these.
Two significant things happen at 4 months old:
- Baby leaves the newborn phase of being designed to just eat and sleep. You have to start working hard to get baby to sleep.
- Baby quite suddenly needs lots more calories. You have to start working harder to ensure baby gets plenty of milk.
My DD's milk intake went up (permanently) by 25% at 4 months old. That is not just a bit more milk, it's loads and loads more. But this comes at an age when babies get distracted easily. So parents end up having to work at getting the milk into baby when previously it came easily and they could just 'go with the flow'.
Likewise sleep. From the newborn who's basic biology is just to sleep, so milk sends baby to sleep. Suddenly the world is far more interesting (like being distracted when feeding) and you have to start working hard to getting baby to sleep, rather than just 'going with the flow'.
So I don't agree with the concept of the 4 month sleep regression. Well I do. Babies definitely get harder work somewhere around 4 months (as they leave the newborn phase). But it's not a 'regression' and it is not something that just happens and you wait it out.
It is just a time when lots of changes happen - possibly the first time in baby's life that significant developmental changes happen - and those who carry on as normal and don't change tactics along with their baby are likely to wait a longer time to come out of the other side.
OP - From your posts here, your baby isn't getting enough daytime sleep. Good sleep promotes better sleep and poor sleep spirals to cause worse sleep. If your naps are short then aim for no longer than 90 minutes awake between naps. Short naps are fine, as long as they are frequent.
The EASY structure will help encourage frequent naps and feeds. I would follow a 2h-2.5h EASY cycle at this age:
Eat - Full Feed
Activity - No more than 90 minutes from waking, more like 60 mins if it takes a long time to get baby to sleep)
Sleep - I favour dummy and bouncy chair for daytime naps. Aim for 30-45 minutes, or until baby wakes naturally.
You time - then when baby wakes start again with Eat, Activity, Sleep, You. Repeat, repeat, repeat.