Dark spots between my breasts?

So I have this dark spot / red rash (because ive been scrabbing it hard ) in between my breasts. Ive heard it could be fungus because of sweat using the wrong bra size , etc or Aconthosis nigricans because I am overweight etc . I think it might be A.N Im scared im trying to change my diet but what else could i do to get rid of it or to make the darkness disappear I tried putting talc so its not wet and washing it and exfoliating it even though its irritated please help