It sounds like you are having a tough time. My DS who is now 4.5 months went through a similar reversal in sleep at about that age. For me i cuddleded him to sleep when i had the time or put him in a sling and let him sleep. At 4 months i strarted wrapping him again for day sleeps (i feed to sleep). So now he has 2 sleeps a day, with a total of max 2 hours sleep during the day. Goes to bed at 7pm and wakes up for the day between 7 - 9am. he does wake for feeds during the night but that is pretty irregular for times.

My DD used to sleep 2-3 hours for each sleep so this not sleeping is a bit strange for me too. I have tried pram, car, sling to get him to sleep more but he doesn't sleep.

I haven't been much help butI guess my point is if they don't won't to sleep forcing them to sleep is just stressful for you both. Some babies just need less sleep. I don't believe my DS is a self setteling problem as he must wake and go back to sleep overnight at various points. For me the whole self settling thing doesn't work as I feed back to sleep overnight. I went through all that trying to do self settling with myDD. All it did for us was cause stress.

hope you find something that helps soon.