Well... your pups only 5 mo's so biting can be teething or playing. Whichever the case, you have to be firm when telling him NO when he does things like this. I let Meka play with me like that... And by saying Ouch, she will soften her bite, and if she's too hyper... then, I tell her NO firmly and she will stop. They dont know until you teach them
Patience...