I have acne all over my shoulders and back. how can i treat this?

Systemic Rx: This always requires systemic treatment, either the oral contraceptive pill if you're a lady who can take it, or an antibiotic that's right for you (tetracycline or macrolide), or if it is severe enough, accutane, which only a dermatologist can prescribe. The latter is unpleasant, somewhat dangerous, extremely effective, and in my opinion worth it. Good luck.