What could cause your period to be 14 days late other than pregnancy?

If you recently had a drastic change in your diet, it could affect your period as well. This happened when I did a juice fast for a week and then a meatless diet the following week. My period, which is normally regular, was delayed for about 2 weeks. It went back to normal soon after though. That being said, I will not attempt such long bouts of drastic food changes for a long time after that experience.