5 week old sleeping for 8+ hours?! ?

He sounds fine! Lucky you having a contented little baby like that! Do make sure that you are leaving at least 3 hours between the start of one feed and the start of the next. Darken the room for naps and night time and keep him in a reasonably noisy social atmosphere during day this will help him figure out day is for play and night is for sleep. Gina Ford does a good routine for this problem. I got my little one a fisher price gym with a mirror and mobile built in at 3 weeks when this started happening with her and it also did the trick to keep her awake and stimulated in between feeds and naps. Good luck.