[COLOR="Navy"]It's normal for you. If that's the only time you have this, then I wouldn't worry. It's just your bodies way of telling you that your menses are abaout to start.
When I used to get my period, I always ached behind my knees. It was so awful that I could hardlly stand it. That was my normal announcement. It varies from woman to woman...and it changes after you have children.
But I think you are just fine
BTW try taking some naproxen(aleve) and see if that helps[/COLOR]