The best treatment is in three steps and uses only over-the-counter products. To get started, you'll need a gentle cleanser, plenty of 10% alpha hydroxy acid, and lots of 2.5% benzoyl peroxide. In my experience, an alpha hydroxy product which contains licochalcone works best.
I'm with feelings. This may not be acne, but may be a rash! Don't start putting anything on your body that may further irritate your skin. Maybe see the doctor (as an entire body rash seems like it could be serious).