What Causes Pimples On Face, Back And Chest?

hi,i am facing lots of pimples on my face,chest,back and forehead.i had not even 1 on face and chest but i had on my back from last 5 yrs.according to me pimples on face and chest started when i took weight gainer protien shake.i want to know is it the reason and can u tell me the treatment please.