Suggest Treatment For Itchy Skin Rash

     Last week a friend visited me and while he was here, he complained of a skin problem--an itchy rash. I now have a similar condition, which I believe I caught from him. I visited my GP who disagreed with my opinion. She prescribed Aqueous Cream, which I am applying regularly, but so far without effect. The rash is all over my back, and is extremely itchy. I'm in my 70's, and have never been prone to skin problems before, and I'm pretty sure it's an infection, rather than an allergy. I would appreciate any suggestions!
Thank You