What Causes Spots Between Breasts?

Hi I'm pearl milnes and I have spots between my breasts with no lumps. On one downside they're quite soft on one of them and some horrible puss came out on one night and it was really disturbing. I've tolled my mum and she recomenended that I should use sudocremme but I'd like to know of how I got them because I've never had problems with my boobs.