Hi there! He's really cute!
1) GSD and husky is all I see in him but then again I'm no expert ha
2) have you had him checked out by the vet? He could be sore, If not some dogs just don't like others to be too close to them!
3) I, honestly, would stop doing that. He doesn't seem to like it. Sure dogs do it to each other but you're not a dog and he knows that, maybe he doesn't know that you're trying to play? Either that or he's just playing back, you're biting him so he'll do what he would if another dog was doing it to him, which would be to play bite back.