For virgins, menstruation flows from the hymenal hole to the outside of the vagina, while for women who have had sex, it flows directly from the vaginal opening. Whether you have had sex or are a virgin, menstruation flows out of the uterine cavity and then into the vagina. This is because menstruation is due to the cyclical shedding of the uterine lining, which then flows out of the uterine cavity. The normal menstrual flow is usually between 20-60mL, and menstruation clears completely in 3-7 days. Since it may be difficult for a woman to get her period out when she is not having sex, it tends to stagnate inside the vagina, so there may be significant stomach pain at this time.