Dear Sugar
I have always had an irregular period, so being a couple days late is never a concern. However, this month I am 3 weeks late and I am worried. Is it normal to miss a period for no reason? I have already taken three pregnancy tests, (even though I haven't had sex in about two months) and of course they came out negative. What's the problem? Late Lettie

Dear Late Lettie
If you are always irregular, then a week is ok. But 3 weeks is a long time. Has this ever happened before? Have you been spotting at all?
Pregnancy is the 1st most common cause of late periods and stress is the 2nd. Since you've ruled out pregnancy, is there something in your life that is particularly stressful right now? If so, your periods should return when the activities or situations that are stressing you have been eliminated. Try your best to eat healthy and to keep your weight steady. If you are overweight, make sure you are eating a balanced diet as well as continually exercising. If you are underweight, try to eat more caloric foods. Lastly, if you follow a strenuous exercise program, cut back until your period returns. If you don't get your next period within 6 weeks (so 3 more weeks), it's time to call a doctor.