Small sore lump under ? women only please....?

every once and awhile I will get a small VERY sore lump (about size of a dime) under my . feels like it's "inside" the flesh of the . the lump can't be moved around, it stays in the same place. then it will disappear but reappear weeks later, etc. what is this?? I have very large natural also size 48DD, could that be the problem.