Acne does not occur on the scalp. The commonest site for acne is face, trunk and proximal upper arms. Probably your condition is different one and may be of some kind of follicular pathology affecting scalp. It can be a simple condition such as folliculitis, seborrhoeic dermatitis, furunculosis, or more difficult conditions such as folliculitis decalvans, tinea capitis, dissecting cellulitis, etc. Unless you are physically seen by a dermatologist, it is difficult to pinpoint the diagnosis and thus suggest any kind of treatment.