Many women have cramps along with their periods. The pain can range from mild to very painful, and it can vary from month to month how much they hurt and how long they last. Many—but not all—women also experience PMS (premenstrual syndrome). PMS is the name of the group of symptoms that start around 7 to 14 days before your period begins and usually stop very soon after your period starts. No one knows for sure what causes PMS, but it seems to be linked to the changes in hormone levels that happen during your menstrual cycle. If you experience PMS, you may experience one, some, or many different symptoms. Some months your PMS may be worse than others or you may have no PMS symptoms at all.