My son started a bit of that around that age. I had tried giving him some cereal once or twice before than, but in my experience, he still woke up every four hours at night and ate the same amount... so it didn't sustain him any!
People told me he could be teething. Is he slobbering to the point where his shirts or bibs are just soaked with drool? Is he trying to bite everything he can reach... your hands, your nose, your chin, chewing on his pacifier, toys, etc? Does he push the bottle away sometimes, but after a few minutes, drink from it? These were some of my son's signs of teething. Sometimes it hurts him so bad, that he doesn't eat at all.
If he's not really showing definate signs of teething, cause all babies are different, I would bet that he is going through a growth spurt. Babies suddenly consume a lot more than usual when they go through this. My son was like this for about a week, then it started to go back to normal... or into a more predictable schedule I should say. I would just keep doing what you are doing... talk to your doctor about when they believe you should start babyfood and cereal... and feed him as much as he wants. This will pass, and come back again, then pass, and go on that way for a while. Before you know it, you'll wake up freaking out because he didn't wake up... lol. I did that a number of times.