What Causes Pimples On Back, Chest And Shoulders?

Hello I have a flabby like skin tag above my rectum area, never hurt or irritated me untill I tried to pull it off. Recently today it looks as if it was filled with pus now. I have a ver bad acne problem on my back/chest/shoulders, could this be a hormone issue? or a gland issue? I do work out alot as well.