Itchy- help

I am very clean and have not had any unusual discharge or any other symptoms, but last month and this month near ovulation time I am finding that I am itchy between the labia, and just at the vaginal opening. Last month I thought it may have been a yeast infection, but I didn't treat for one since there were no other signs besides the itch. It went away by itself when I got my period. Its now 2 weeks later and I'm ovulating and itchy again. It can't be sex related, and I have not changed soaps, detergents, or anything else...ideas/suggestions??