I don't know that anything is wrong with you. Are you involved in a lot of sports? Are you very lean? I was very "late" in getting my first period. I don't think there is a normal age for someone to get their first period, but you should speak to your doctor about it if you are concerned. If you are healthy, maybe your body is just not ready yet?
Sometimes it takes the body time to adjust. My daughter is 14 got hers in april and anything she has had since has not been regular and she is also very slim and athletic so that might be why. I would not worry. Sometimes it just has to run its course.