One of the most common gynecological problems is an irregular menstrual cycle. You didn't mention how long you have been menstruating, but a female's period will usually tend to be irregular for at least the first one to two years of her cycle. It will gradually become more regular. Before you jump to the conclusion that you're irregular, it's important to remember that being regular doesn't mean your cycle is the same number of days each time. Each woman has her own cycle that can be every 21 to 35 days. It is also not unusual to skip one or two periods a year; however, it is unusual to skip more than that.
There can be several causes of irregular or missed cycles:
TeenHealthFX recommends that you discuss your period with your doctor, preferably a gynecologist. It's a good idea to track your periods on a calendar and then review it with them. You can do this by marking down the day your period comes and the number of days it last for. Do this each month. Also, they can evaluate your level of exercise, eating habits and menstrual history to determine if your cycle is normal for you. If you don't have a doctor and live in Northern New Jersey, you can call the Adolescent/Young Center for Health at 973.971.6475.
You can check out some of TeenHealthFX answers to other questions about irregular periods. See Extremely Worried about Period, Not-So-Normal Period,
My Period is Irregular and Period Few and Far Between.