Any breed of dog does that behavior at only 3 months old. Hes teething and needs to relieve the pressure. You should get him some nice hard chew toys with nubbies on them for his gums. Also, try small ice cubes. They love them. Just like a teething baby who chews on your fingers and hands. Just he has little razors in his mouth lol. Give him a few months and alot of discipline and love. Good luck and have fun with him
Weve all been there.