How To Treat Itchy Scalp?

I have been battling with an extremely itchy scalp ( there is a red rash and a few bumps; . I thought it might have been due to a reaction to a new shampoo I had started using. I visited a Pharmacist for advice and she recommended Dermalab shampoo ( its a natural shampoo with no artificial colours, fragrances or parabens) -. She also advised anti histamine tablets for the itch ( Xergic 180 - it contains 180mg of fexofenadine hydrochloride) . I have been taking the Anti Histamines for almost a week & have used the shampoo 3 times in the last week, but I am still REALLY y battling and going crazy with the itch. I would welcome your advice.