My son was born @ 36 weeks with a birth weight of 6lb 9oz (currently dropped to 6lb 2 1/2oz). He is currently 10 days old and seems to be feeding infrequently. He'll sleep for 3 1/2 to 4 hours or more at a time and seems to have no interest in waking up any sooner to eat. Is this too infrequent? I'm just concerned he may not be getting enough to gain.