Parakeet recently started biting, why?!?

I have had my parakeet, Huckleberry Phineas, for almost 3 months. I got him at about 6 weeks old and he is already talking saying "Good Boy" and "Pretty Bird" and "Uh Oh". He is hand tamed and usually a good bird. For the last couple weeks he has been so stubborn and when he doesn't get his way he will chomp down on your finger. Any way I can stop this before it turns into a bad habit? Thanks alot!