What Causes Constant Vaginal Itching?

I have had constant vaginal itching for about 1 1/2 years. I ve talked to my primary care doctor about it. she is the one who does my paps every year. She did some bloodwork and seems to think I could possibly have genital herpes. She did a HPV test and said I am at high risk. The only sex partner I have had in 40 years is my husband. Why would this just be showing up. The itching seems to be worse at night and it ressponds pretty well to monistat cream.