There's as much variation in menstruation as there is in women. One sister has her first period at 11, the second at 14. One woman is "as regular as clockwork," another's cycles fall randomly across the calendar.

There seems to be no rhyme or reason to it. Yet in most cases, this is all perfectly normal.

But when any menstrual symptom — pain, heavy bleeding, spotting, missed periods — begins to interfere with your life, it's time to seek medical attention. Most problems are relatively uncomplicated and respond well to medication or simple surgical procedures. Others could have more dangerous consequences if the underlying cause is not treated promptly. If you have any doubts about your menstrual problems, see your doctor.