I've had some problems with pimples on my back, not full blown bacne but a fairly persistent spattering of them over the years - I started taking Oregano oil for a tiny psoriasis patch (thanks for the genes, mom!), which subsequently cleared up, and much to my surprise it has greatly helped my back, too. Garlic can help too, although is far stinkier and may interfere with your enjoyment of frags.
I should add that the oregano oil I take is diluted,. It's this stuff, in fact: http://www.vitacost.com/NSI-Oregano-...F-835003006847
I take it internally, but it also works topically, but I'd suggest diluting it down further as at that concentration it can cause an extreme burning sensation, and can in fact, on delicate skin (i.e. the nose) cause burns. DO NOT take it internally if you are on other blood thinners though, and ask your doctor if you are on any medication, as it does thin the blood! Here is a lot more information on it, if you are interested: http://www.answers.com/topic/oregano...oil?cat=health
Tea Tree oil, more specifically Tea Tree Manuka, is also very good, and is much milder on the skin (and the manuka variety, while being a far more potent anti-fungal/bacterial edit: than normal tea tree oil, also smells rather nice).