My little bloke was like this even in hospital. I asked the midwife if I should set an alarm to feed him so he didn't sleep to long and she said "Don't worry they ALWAYS wake up and don't sleep for longer than 5 hours." He slept for 6 nearly 7 hours and then the midwife got cranky with me 'cause I had let him keep sleeping. Well I was asleep as well!
I had to set alarms during the night so he ate and I tried desperately to do demand feeding but he just never demanded.
He lost weight and was a bit of a problem in the early days.
If I were you I'd wake him and feed him and try out a bit of a routine that suits you. Leaving it too long between feeds can also mean you don't produce milk at the rate he needs.
Good luck, people just don't understand how tricky they are when they are not the hungry type!