Q&A: Picky Eater?
If baby is gaining weight well and seems satisfied, he's probably just fine. Sounds like you have a super-efficient nurser on your hands. Some babies are simply able to get more milk out in a shorter amount of time than others (and usually, this skill is developed over time).
However, if his weight gain is slow, be sure to get experienced, hands-on lactation assistance ASAP to help you evaluate (and hopefully solve) the issue.