Not Gaining Weight

Ethan loves to sleep...like a pig. It takes me a long time to wake him up. He rather sleeps, but I have to wake him up to feed or else he won't gain weight. First, he didn't pee or poo for over 12 hrs so we were concerned. When nurse checked him, his diaper was dry, but when doctor came, sure enough, he pee and poo (on Thursday, his weight was 6 lbs and 4 oz). His birth weight was 6 lbs 12 oz.