Need advice on getting my son to sleep better naps and at night

My son is 20 weeks old tomorrow he used to be amazing at sleeping only woke 2 times maybe 3 a night got up at 8 or 9 am even tho he had a late bedtime of 1030 or 11 it was perfectly fine. Now this last week I havent really slept unless in the rocker which i feel is unsafe and is just painful to my arm and neck. He wakes ever 30 mins some night others its 1 hour to 1 and a half hours he doesnt want to nurse just wants me to rock him back to sleep i can do this in 15 mins then hes out occasionally its a burp that wakes him other than that i dont kno what it is unless it's feed time what bothering him so much im at a loss and very tired