I took Valtrex for a while, I don't recall exactly, but probably a year or more. Insurance wasn't too happy with the cost, but I finally stopped when I had some elevated liver enzymes. I can't say for sure how much it helped. HHV-6 and some other viruses continued to be active in that time period.
As we all know, we are all different. It hurt @Who Me? , it didn't hurt or help me tremendously - maybe it will help you! Good luck.