I have had an itchy rash on the back of my head for about 8 months. It seems to move around. It was at the base of my head, moved to behind my ears, then moved down the middle of my back. I saw a dermatologist that ruled out exczeyma, psoriasis and mites. She perscribed a steroid cream that did not help. At times the itching is unbearable. I have switched to all sulfate free hair products and it's still there. Help???