I Recently Was On Valtrix For Shingles Which Were Caused

I recently was on Valtrix for shingles which were caused from trauma of a severe poison ivy attack. I started breaking out in big red whelps and was in horrible pain. My Dr. gave me Prednisone and it helps but I am still itching. I am taking a benadryl every 6 hours and that helps to some degree. How long will this last and is there anything else I can do?