I have pimples in back of my head what can i use?

Skin lesion in head: Skin disorders need to be seen. What you describe as "pimples" may be many things. Common lesions in the scalp could be impetigo or piodermititis, fungal, but even herpes zoster or herpes simplex, psoriasis, lupus, skin cancer, scabies etc. Show it to a dr. Or dermatologist.

Acne keloidalis: It sounds like you have acne keloidalis nuchae. Treatment can vary from antibiotics like Doxycycline to steroid injections. To be sure you should see a dermatologist.

Scalp Folliculitis: Folliculitis is the medical term for the infection and inflammation of the hair follicles. This condition can affect the hair and skin on any part of the body, including the scalp. Scalp folliculitis is characterized by the appearance of small, white or yellowish pustules, that resemble acne. The pustules can be quite itchy and painful at times.