Infection At Back Of Head In The Hair

i have been suffering from some sort of infection at the back of my head, in the hair portion. It spreads around and i have consulted many doctors and also given a sample for test. Results turned out to be nothing and initially with anit biotics they vanish but soon they return. I was adviced to use external medication like a medical shampoo, given by a doctor. but still the problem persists. I would be very grateful if you can suggest a solution to the same. Thankyou.