I Have Had A Raised Red Rash That Started On

I have had a raised red rash that started on my legs and has spred upward to my buttocks. The spots started as small flat red dots that started to feel slightly raised and bumpy. Heat seems to make it redder, but it does not itch. I have not done or been exposed to anything different and I do not have any other symptoms. I was given a prednisone pack and cortisone cream. I have 2 days left on the pack. The rash is not much better