[mscat]

IMO, I do believe a lot has to do with him being taken away too ealry from his littermates and mother. He did not have enough time to learn propper social skills training at a crucial period of growth and development. now, you are going to need to teach him. When he bites too hard, Let out a High pitch Yelp like a puppy would , instanly pull your hand away , and play time is OVER! Walk away, ignore him. Do not reward him at all for biting you .Do this each and every time he bites. He will soon learn that biting is not acceptable behavior. only when he plays nicely, will you play with him. STOP playing, YELP, high pitch sound, and it's over. You need to do this consistently in order for your puppy to understand and to be taught correctly that biting is not ok.
My Suzi play bites, however, never hurtful like this. In a month or two your puppy will began going through the teething stage. This is different though. He will want to chew on everything. Then you will need to provide safe chewing toys/Bully sticks for your little guy. Also, this may be good for him right now as a distraction. If there are any new teeth coming in at all he is going to want to want to chew and bite on something . Your going to want to be prepared. He is very young at only 3 months, 12weeks old. right now he is just a very playful, little baby puppy.