My baby won't sleep at night as well as he used to?

My son is about 19 weeks old and up until the last two or three weeks he's been an amazing sleeper where he'd eat a lot around 10:00, sleep, and then only wake up around 4:00 drink another 6oz, and then sleep until late morning. Now he will drink a lot before 10 like usual, sleep, wake up at like 1:30 to eat, wake up at 3:30 to eat, wake up at 5:00 to eat, and then from there he's up pretty much every hour to eat a little bit. I'm not getting enough sleep. What do you think the problem is? Should I be giving him some cereal now? He's a big guy at about 19lbs and has been having breast milk and formula 50/50.