An early period may occur during puberty and perimenopause due to hormonal changes. Other possible causes of bleeding before a period is due include endometriosis, polycystic ovary syndrome (PCOS ...

A period is considered “early” if menstrual bleeding begins within 21 days of the beginning of your previous period, according to Monte Swarup, M.D., an OB-GYN in Chandler, Arizona and founder ...