What Causes Raised Rashes On Arms With Elevated White Blood Cell?

I am a 58 year old female that developed a raised rash on my arms last Wednesday. As the day progressed, I developed a small red bump rash. Urgent Care prescribed amoxicillian and prednisone in 10 mg 3 times a day. Friday was much worse and large spots that resembled a bruise was developing on my legs and top of my feet. Family doctor sent me to ER for blood work. Dr diagnoised Vasculits in the legs and not sure what raised rash was. Went to dermatologist Saturday increased prednisone and ordered more test. White blood cell count is slightly up Dr thinks may be the result of cortisone shot at Urgent Care on Wed. Blood work good except elevated white blood cell count. Any thoughts?