Pant Bitting Puppy

Well, you've got a pup and you've got a part LAB pup...labs tend to stay pups for years from what I've been told, and puppy nipping is quite normal.
 
He wants to play....in the doggie world, one initiates play by nipping.  Pushing him away is seen, by him, as a sign that YOU want to play too.  Since you aren't giving him a clear out "that hurts dang it" he doesn't know that he's hurting you.
 
When I foster a litter I literally wear shoes and thick socks and old pants ALL the time, and wear a fanny pack stuffed with good chew stuff.  Ive been known to cross a room totally ignorning that I'm attached to six or seven pups, and carefully leave the room, never saying a word to them.  Typically, I will give them a gentle "eh eh, no bite" give them a toy and tell them THIS is what you can bite and then praise for chewing on IT instead of me.
 
Time, patience, and gentle consistency is what it takes to get through this time.....
 
Oh, and welcome to idog

Has anyone else had this problem and how did they get around it. And is this something I should be really worried about or is he just being a puppy?

 
He is just being a normal puppy. As for how to handle it, I'd echo Glenda's advice.

It sounds like you have a persistent pup that likes to play and has gotten the message that you want him to.  As you have noticed at puppy class, dogs can play rough.  The secret to having your pup learn that people don't, is to avoid pushing your dog, or even acknowledging him.  If he is reactive, don't yelp, just leave the room without looking at him or speaking (even if you have to gently squoosh his little nose in the bathroom door to get him off your pantleg []).  Wear old clothes when he is around. []  I know it's irritating, but eventually, he will "get" that his playmate (you) disappears when he puts his mouth on the human.  Even pups teach each other this lesson, and play is suspended for a second when another pup yelps or leaves.  Even though they go right back and try again, the next nip might be just a tad softer, until you see pups playing open-mouthed leaving only spit on their playmates's heads, and not toothmarks LOL.  

just leave the room without looking at him or speaking (even if you have to gently squoosh his little nose in the bathroom door to get him off your pantleg )

This is one situation where I'd go straight to gently squooshing his little nose. This is exactly when most of my dogs learn "No". Border Collie puppies LOVE pants legs and shoelaces - it's the ideal time to teach them that Not All Things Are Herdable.

But it's a personal choice. If you don't feel your dog needs to learn that People Say No sometimes, the methods mentioned above also work quite well.

I would echo all of the above advice.  But I also don't want you to think your puppy is trying to be D0minant.  He's just being a puppy.  

Thanks for all the replies.  I have tried some of them and they do seem to be working...
 
Thanks