E.K.
I strongly recommend waking him up to eat at that age. I had problems with both of my girls not putting on enough weight in the first few months and I think some of it had to do with me being afraid to wake them up all of the time. Yes, a hungry baby will wake up to eat, but I think a baby who is comfortable, warm, and feels safe will also want to sleep a lot. Plus, if you are nursing, your milk supply will be much better with regular feeding sessions.