What am I doing wrong?

My son is 4 months, 3 weeks old (born at 36w6d) and he is still eating every two hours pretty much. He was sleeping through the night (9p-7a) about a month ago, but now he’s going down around 9:30p and waking up around 3:30am to eat and then the every two hours cycle continues throughout the day. I’ve tried increasing the amount in his bottle (he gets expressed breast milk) but he doesn’t finish it, plus he has untreated acid reflux and terrible, painful gas so he shouldn’t have huge bottles anyway. He is within the normal range for his weight, but he is a little short. I just didn’t think he’d still be eating so frequently at this point. I mean I feed him whenever he’s hungry, I just think he’s probably eating a little more than he should be, and it’s making it hard to get on a routine, because he’s up, he eats, he has to sit up for 30 minutes after a feeding due to the reflux, and then repeat. And it’s making it hard to do anything because by the time I feed him, sit him up, and get him ready, it’s almost time to start over again! I think I’m messing something up. Help!