Rash developed Sunday. Very itchy, bumps that look like large blisters, spreads quickly and the rash has heat in it. It has spread all over my body, itches and looks bad for several hours, then clears, then reappears in other areas. Using Benadryl and hydrocortisone cream. Slight relief. Had a mammogram and pelvic ultrasound last week. Could this be a reaction to those procedures? Also used a different soap two days last week, I tend to think that was the trigger. I believe this rash to be hives. I am covered in rash from my neck to my knees.