How do I get rid of these annoying pimples on my scalp?

I have small little painful pimples all over my scalp. They are so annoying and I can't get rid of them. I have tried washing my hair with every shampoo available (Nizoral, T-gel, T-sal, aveeno, pantene, Selsun, Selsun naturals, head & shoulders) and have even been to the dermatologist. He couldn't even help me. He gave me antibiotics which cleared it until I stopped taking them and they came right back. Does anyone have any advice??? Maybe a decent shampoo or something that helped?? I have also tried the apple cider vinegar method and tea tree oil...Didn't help either.