I have shingles, no pain but it is extremely itchy! Does anyone know how long the itching will last?

I'm 21. The shingles are on my back and chest and I had the itching for about 4 days now. I'm on Valtrex, and none of the itch relief medications are working(Aveeno bath, calomine lotion) It is really unbearable. Does anyone know how long the itching will last?