I Am Experiencing A Rash And Itching. It Started The

I am experiencing a rash and itching. It started the first of April in my scalp. No bumps or redness. Then about 10 days ago I got a rash on the inside of my elbow which spread to the outer elbow and down my right forearm. I now have it on the outer left elbow and forearm. My abdomen started itching and I have the rash there as of this morning. My thighs are starting to itch too. I have been to a dermatologist who prescribed a steroid to squirt onto the areas on my scalp. I went for a second visit when it appeared on my arms. She saw nothing in my scalp but could see the rash on my arms. She could not give me a definite answer as to what is causing the terrible itching and rash.