Hi there,
What are your awake times now? Short naps can also be developmental and we also battled with short naps at that age. Also there is a big sleep regression at 4 months, which doesn't help when you're trying to set your LO on a routine!
At 4 months, we had a good morning nap (1.5hrs), followed by 2 shorter naps and an earlier bedtime. I used to try and keep the E's 3.5hourly (mine is breastfed and wouldn't have gone 4 hrs then) and I relied on 1 good nap in the morning and the rest of the day was hit or miss (the afternoon nap). Eventually when we dropped the catnap around 5-5.5months, the afternoon nap extended. I used to take mine out of the house to extend her A time
Could you post what your last couple of days have looked like? When he wakes at night, how do you resettle, have you tried leaving him to see if he will go back to sleep?