Honestly I've found that my body acne is mainly caused by diet and hormones. Eat simple, natural foods, nothing processed, and things should definitely improve a bit. But that can be expensive.
Shower once a day, with a sulfur soap (stinky )
Drink tons of water, and I mean TONS.
Lightly exfoliate at least once a week.
Use warm water in your shower, hot water can actually CAUSE acne.
Get enough nutrients, maybe take a daily multi, preferably made from natural sources.
MOISTURIZE! I can not stress this enough! It helps so much. Use something hypoallergenic, and non comedogenic. Something natural is best, I use HEMPZ.
Get enough sleep, and at the right times. Go to bed early. Seriously. This allows your body to heal itself and balance hormones.
Change your laundry soap to one free of dyes, and fragrances. Never use fabric softener. (Major Body acne culprits).
Have enough Omega 3, 6, and 9. Ingesting hemp, or flaxseed oil will help with this.
Don't let your shampoo or conditioner touch your body, ever. You may want to try a sulfate free shampoo.
Don't wear anything twice on the afflicted areas.
CUT CAFFIENE! All of it. You could also try removing soy, dairy, gluten, and citrus, so see what foods you are sensitive to.
Stay away from acne products, like BP. They works for a short period of time, and then make your skin worse in the long run.
You could try soaking in a sea salt bath.
I'm in the same battle girlie, and it sucks, I haven't worn a tank top in years.