Your board-certified dermatologist may recommend a combination of oral antibiotics, topical prescription creams. Keep in mind that all benzyl peroxide products can bleach clothing but can be synergistic in allowing post-inflammatory hyperpigmentation (PIH) when used in conjunction with topical retinoid and/or hydroquinone bleaching cream. Avoid non-organic dairy products as well as processed foods that are high in sugar contact. Make sure that you take a shower or wipe the sweat off after working out. Hibiclens soap to affected area during shower can be helpful to minimize bacterial overgrowth but keep it away from your eyes to minimize irritation. Accutane or Photodynamic Therapy (PDT) are viable alternatives as well if conventional therapies fail to help you in a satisfactory fashion.
The problem is that your skin hyperpigments easily, causing even minor acne pustules to leave long-lasting dark spots. First, regular acne treatments with a retinoid like Tazorac 0.1%, Differin 0.3%, or Retin A Microgel 0.1% will both prevent acne and begin to fade the discoloration. A topical antibiotic short term for 3-6 months may be helpfull too. Your dermatologist has several to choose from depending on your skin type. Lastly, Theraplex peels are a great adjunct in my practice for PIH and acne.
Back and buttock acne can be difficult to treat. Occasionally, these outbreaks are not acne at all and are "folliculitis" . Folliculitis would be acne like lesions, ie pimples, overlying a hair follicle. Difficult to treat cases may require oral antibiotics however mild cases may respond to The Pimple Clinic products that are safe, non prescription anti oxidants that will help get rid of acne lesions that are superficial and less nodular.
Acne on the back is very difficult to treat with topical medications such as benzoyl peroxide, retinoids (retin A, tazarotene etc) and antibiotics, oral or topical. In most cases, oral Accutane for a 20 week coarse will clear 80% of patients forever. The program is called I Pledge, is government regulated and strict, but it works. Most dermatologists can assist you with this.