Most women’s periods come every 21 to 35 days. If yours doesn’t arrive around the same time every month, or you skip some months, it might mean that you have too much or too little of certain hormones (estrogen and progesterone). If you’re in your 40s or early 50s -- the reason can be perimenopause -- the time before menopause. But irregular periods can be a symptom of health problems like polycystic ovarian syndrome (PCOS). Talk to your doctor.