How can I tell if my rash is of Poison Ivy or Shingle source?

I had what I thought was a persistant Poison Ivy situation but the third doctor I saw, which happened to be a dermatologist,explained my condition as Shingles and Poison Ivy. So I’ve stopped the first cortizone cream. I’ve started the antihistimine, the steroid cream and antibiotics. Since he diagnosed me with both. I wish a doctor would take more time to explain the how’s and why’s. So here I am…. Ciao!!