Do you have an ex-pen? What I would do is as soon as he starts mouthing, whether painful or not is say ouch, and put him in his pen. Not as a form of punishment, but as breather for you. The ex-pen is great because it only has what you put in it, so there is nothing dangerous he can get into and hurt himself with. Put him in, do 1 chore around the house, then try again. It'll keep your mind distracted instead of fuming over the chewing problem, and he'll see that he gets no attention for mouthing. It will take time but he will eventually understand that play time is extended if he doesn't use his mouth on your hands/feet/shoes, etc. I hope this helps!
