It shows up roughly every four weeks, decade upon decade, but how much do you really know about your period? Did you know, for instance, that a normal cycle can range from 25 to 35 days long? Or that calcium and vitamin D may help ward of PMS?

Gynecologists say that they frequently get questions from women who misunderstand their cycle, and they've shared the most commonly asked questions with readers.

So if you have a burning question about:

• PMS
• irregular cycles
• getting pregnant during your period
• being pregnant and still getting your period
• toxic shock syndrome

click here to have your questions answered!