C.
I am having the same thing with my DS as well. He is 15 weeks old. I think I figured out he was still hungry so I feed him more during the day. I also give him a bottle or part of a bottle when I go to sleep around 11pm. That way he may wake up at 4am and then sleep until 7am. I do put cereal in his nighttime bottle at 8pm. It seems to help and i have been doing it for about 3 weeks and he has been fine.
My trouble with sleep is naps. He gets tired about 1.5 to 2 hours after he wakes up but is a BEAR to get to take naps. It's about a 30 minute process but I KNOW he is tired he yawns, rubs his eyes and his eyes will close then snap open they close ....
Good Luck!!