Can you please help!??!!

Our son is 5 months and a great baby all day. He is on a 3.5hr easy routine right now - we are trying to push him to 4, but that has been hard. He's doing one cycle at 4 hours. He is napping great, puts himself to sleep, no props, etc. etc.
But the nights are making me crazy! He is still waking up once or twice even to eat. But they are different times every night. One night he'll sleep until 4am, one night he wakes at 1am, then its at 2am, then last night it was 12 and 4! What is the deal? How do I make this stop?
He DOWNs the bottle. We usually try to see if we can comfort him first, but it becomes obvious that he is really hungry. I have tried to add more ounces to his bottle, but he doesn't take anymore than 6oz usually. We tried starting cereal, but that hasn't helped either.
I need some sleep people!!

Any advice?