Eczema Treatment Care

I started getting a really bad rash on my breasts about a month ago that won’t seem to go away. First I tried taking prescription allergy medication and applying hydocortisone and it didn’t help, so I went to the doctor and they gave me a cortisone shot and pills (prednisone) and the rash persists. It is very itchy and blotchy, it is a little bumpy but not as bad as it used to be. I also tired applying a cream that I got previously for contact dermatitis and it didn’t help. I tried applying cream for yeast infection and it also didn’t help. I have not worn a bra or tight clothing since the rash appeared. It’s not warm weather here and I haven’t been in the sun so its not heat rash. Does anyone know what this is and how to make it go away? I haven’t used any new soaps or detergents, I washed all my clothes and bedding, I toke all the pills like I was supposed to, I have had no contact with any sort of plants that could cause this, no new medications, no food allergies.