During their periods, most women experience excruciating cramps, bloating, mood fluctuations, and irritability. Every month, the endometrium, the medical term for the uterus’ lining, sheds, causing what is known as menstruation. The female chemicals progesterone and estrogen, which are released by the ovaries, thicken the uterine lining, which then waits for a fertilized egg to attach. If there isn’t an egg, the lining rips, and leaks, which triggers menstruation.