When I was 15 I missed mine for a month, took two tests that were negative, my mother took me to the hospital after I began having terrible abdominal pain, and they did an ultrasound and found a golf ball sized cist filled with blood in my ovary, it resolved itself and actually happens to a lot of women, so it wasn't very serious. My point is you should definitely go to a doctor regardless, a missed period could be from a number of different reasons. Hope all is well.