How Can Worms Reoccurring After Every Period Be Treated?

my daughter who is 16 has worms im not sure which sort, this has been occurring for a while, we treat them with ovex but after everyperiod (which are heavy and clotty) it triggers off again, she is lacking vitb12 but not aneamic eats loads and is always hungary but is slim. she is always tired and often looks yellow, is often nausiated has log term constipation, do you think the parasite maybe in her vagina aswell as in her bowl, and how can we move forward