What is it and how can i get rid of this scalp rash?

for about 2 years now i've had some spotty rashes on my scalp. they get dry and itchy and when i scratch them, they will bleed or be sore to the touch only to come back as thick white scaly dry skin a few days later. i've been using over the counter shampoo's and prescription medications and it will control the rashes but they will not go away for good. the best thing i've used to control the flaking etc. is Olux foam. can anyone help me? thank you