Up until these stages, women experience years of fluctuating PMS hormones each and every month, causing pre-menstrual symptoms (PMS). These fluctuating hormones regulate the menstrual cycle and subsequently cause undesirable side effects. The main hormones before period onset include estrogen and progesterone. In a basic menstrual cycle, estrogen rises for about two weeks then begins to fall, at which point progesterone begins to rise for about two weeks then falls again. This up and down continues each month.