My newborn is eating around 4.5 oz per feeding?!

My baby is almost 2 weeks old. He was born at 37 weeks. I feed him on demand but if he isn't awake I wake him up every 3 hours to make sure he eats until he's back at birth weight (I think he is by now he has a Drs appointment tomorrow). He eats about 4.5oz per feeding. I almost exclusively pump milk because he just falls asleep on my boob. Is this a normal amount of food? It seems like so much. I can barely keep up. I occasionally have to throw in some formula because he's so hungry.