Hi T.,
I am also a new mom to a little girl who will be seven weeks old tomorrow. First of all, I think that all babies are different and nothing that works for one will work for all. My daughter does not have reflux although she does spit up sometimes. I just wanted to offer you encouragement because I was beginning to worry that she wouldn't sleep more than 3 hours at night because everyone kept telling me about their babies who did it earlier and because I started back to work last week and really need the sleep. Starting on Saturday night and every night since then she just started sleeping 6 hours, even when she has had a small feeding. I was completely amazed and shocked (and ecstatic!!). I think babies are going to do what they want when they are ready despite all of our best efforts to try to make them do what we want.
My daughter always falls asleep while eating so I try to burp and change her diaper in the middle to keep her up a bit longer. I don't really think it's a good idea to force your son to eat more than he wants to. Just be patient and try to appreciate these times - he will be big before you know it. Good luck!
P.S. Despite what your ped says, I think that is a reasonable amount. From what I've read, babies at that age consume between 20 - 30 oz per day so if you are feeding 8 times (every three hours) that would be about 3 - 3.5 oz per feeding. Seems like he is right on course. If you try to feed more than that, you are essentially putting him in a food coma (if you know what I mean). You are over-filling him so that he is just so stuffed that he has to sleep. This does not seem really healthy to me... Just my opinion.