Aggression and Bitting - HELP!!

[MelissaG]

I don’t know what to do…. I have a labradoodle puppy that’s 15 weeks old and he is normally great. He sits and waits for his food, if I use the off command with toys, treats and my clothing he refrains from touching them until I say so, he sits at the door to go out, he gives a paw for all treats, and rings a bell to go outside. We go for walks outside, we use the treadmill, we play fetch. We also go to obedience school and he’s an angel. But at least once a day whether it’s outside playing or just hanging out he start to bark, then growl, then he jumps ups and bites me… If I ignore him he only runs around more quickly and then lunges to bite me….If I force him to sit or command him to sit, he does so but then a few minutes later he’s back to growling, lunging and bitting me….

How do I get him to stop this behaviour? Why is he all of sudden so aggressive? Any suggestions would be greatly appreciated.