What Could Be The Reason For Having Itchy Dry Irritation On My Vagina?

I recently had itchy dry irritation on the outer lips of my vagina. When I itch too much it begins to get sore and a bump forms. The bump is red from irritation but not filled with any puss or anything like that. It's just is either one bump on each side and when I put Monistat on it, it goes away but it happens around the time of my menstral cycle and I am getting worried it could be something serious and hoping this isn't herpes ?