You could use a course of antibiotics along with anti acne creams applied on your back. They will clear up in 2 to 3 months. Once your pimples subside you could start using glycolic acid or azelic acid containing creams for your marks. The skin on the back is very thick so it takes more time to respond than facial skin. A visit to a dermatologist near your should be helpful is solving your problem. The problem is completely treatable. Also, since it is painful we have to rule out a condition called folliciculitis. Folliculitis is an infection of the hair follicles which is different from acne. Pimples are usually not painful on the back. If you have very large pimples which leave pits on the back you may he suffering from acne conglobata which is a severe form of acne. This will require some other tablets like retinoids and takes about 4 to 6 months to clear up. Hope this has answered your queries. Warm regards. Dr. Rajdeep Mysore. Chirag Hospital Bangalore