Did you know? One of the many reasons why periods can be irregular on our list of menstruation facts is stress. Any stress on the body, whether, physical or mental, can upset the natural balance of other hormones. This can result in a late or early period. Stressful life events can cause an irregular period, as can thyroid problems, illnesses such as the flu, certain medications, and switching birth control. Therefore, it is advised that you take time to decrease the stress and take time in your busy day to take care of your physical and Mental Health.