Hi!
My DS likes to play with my nipple too but usually AFTER his feed and he plays with the one he has been feeding from as my bra is always on and he doesn't have access to it anyway.

However, one thing he does like to do is pinch my breast or pinch my stomach (near my belly button) and that was getting painful. He would also do a thing where he would roll the skin of my breast between two of his fingers and that got painful as well.

To help him not do that as much I spent a few days keeping his Nu-Nu (lamb toy with a small soft blanket as its body - IYKWIM) between him and my belly and he stopped after awhile. He usually has to be really upset or really overtired before he'll do the pinching rolling bit.

I'm not sure if that is helpful at all but thought I would share my experience with you.