sounds like he is training you! a common solution to this problem is to say ouch and leave the room! withdraw your attention for a couple minutes and try it again. if your pup learns that biting = no more attention he will likely stop the biting. it won't happen instantaneously and you have to be consistent (meaning every time he bites you get up and leave) but he should catch on pretty quick.

when is he most mouthy with you? when you play?