I've had acne on my back all my life... even though I've never run gear. LOL. Doesn't matter how many showers or what kind of soap I use. It's always there.
My Derm at first prescribed an anti-biotic call Tetracycline. It works great, but the only problem is it makes you extremely sensitive to the sun and prone to sunburns. You have to wear sunscreen and stay out of the sun.
It also messes with your diet, because you have to take it 4 hours before or 4 hours after eating, which, for a bodybuilding, would suck, because I imagine you are eating meals throughout the day.
Because of the shitty conditions and sides with Tetracycline, my derm switched me to an Erythromycin cream. It was awesome and cleared up my shit great. The only problem is, you have to have someone else apply it on your back because you can't see or reach everywhere it needs to be.
I eventually stopped using it though, because like a dumbass, I read the included pamphlet that comes with the medicine and it said one of the possible side effects of the stuff was that it could mutate your DNA?
After that, I just gave up, and now I live with the acne. I don't give a fuck anymore.
Good luck brother.