How To Cure Itchy Red Rashes In The Groin Area?

I started with a red, extremely itchy rash in my groin area a week ago. I was taking Omnicef at the time for a u.t.i so my GYN assumed it was an allergic reaction. Also, nightime cramping in my legs and knees began when the rash appeared. The rash has now spread to my neck, scalp, arms/underarms, bra line, abdomen, and legs. I am taking Prednisone, and Diflucan for possible candida. The rash isn't clearing with the steroid. When I wake up in the morning, the rash is at its itchiest and subsides as the day goes on, but I find new areas where its spread as well. What is this? Do I see an allergist, immunologist or dermatologist? I have no clue.