How To Get Rid Of Scalp Acne Completely?

I have serious scalp acne issue. When i contacted my nearest dermantalogist, he prescribed me Azithral 500 mg. Scalp dermatitis is what he mentioned. Acne reduced but after couple of weeks it increased again. He asked me to get the blood test done to prescribe Isotretinoin 20mg. Acne did reduce on my scalp but it comes back sometimes with full of vengeance. I wash my hair daily with herbal shampoo and use apple cidar vinegar. Could some one help with to get rid of this completely. Scalp acne are riddish spots, once they dry out , they come out in white flakes and dandruff form.