The most common reason for your period to be late is pregnancy, but this isn't necessarily the only thing that can cause this to happen. If you've lost or gained a lot of weight recently, this can kind of mess with your ovaries and cause you to skip a period. Another thing that may cause this is a thyroid problem. The thyroid controls your metabolism, and that can impact your period. Either way, it's a good idea to see your OB/GYN to have them take a look. Try not to worry in the mean time, though.