Suggest Remedy For Skin Rash

I have a heat rash on my skin on right elbow..its a patch of 2 inches..got a small patch of 1 inch on my left elbow and behind my neck. On consulting a dermatologit he says its a sunburn and treated me thrice but never got cured completely. It gets aggrevated when i go in the sun and i start itching. The doc advised me to avoid going in the sun completely. As I m a working lady its pretty difficult for me. I use sun screens and umbralla and maximum try my best not to expose my skin to sun. What should i be doing?