Hi and welcome! RBI is a cutie!!
It seems to me like the biting is part of playing and teething. I've also read that when they are puppies and with the rest of their litter, if they play too rough and they bite their brother or sister too hard, the brother or sister will yelp and of course not play with them for a little bit. So like orinskye said, by saying "ouch" you will let him know that you did not like what he did. Maybe follow it up by not playing with him for a few minutes. Walk away or something like that. I've done that a few times. Sometimes he starts biting back again and sometimes he doesn't. It's all about training them to be good little doggies!
By the way, my name is Brandi and my little Hercules is 4 months.