I am suffering badly with acne on my chest and back .please suggest what shall i do ?

Many options.: Begin with benzoyl peroxide. It's effective and well tolerated for most people. Start with a low strength and increase if needed. With stubborn acne, add a second product with a different active ingredient, such as salicylic acid, alpha-hydroxy acid, or sulfur. But do see a dermatologist; in the long run it's way cheaper than trying all those "miracle" non-prescription concoctions.