At what age did you have your very first period ever?
In the first couple of years of getting periods, it may take some time for your body to settle into a regular "routine". That may mean, hit and miss with the regularity. It can mean still having irregular periods and can be quite normal. It's highly unlikely that you have anything wrong with you at all.
But, first things first. Are you sexually active? If so, have you been using birth control of one kind or another? If not, you really want to talk to a medical professional about the possibility of pregnancy just to be on the safe side.
Next, if the above doesn't apply in any way, have you been under stress lately? New school, exams, tough time in your life, stress with friends, home, family...or, any other big stress that has you upset?
Are you dieting or exercising a lot? These things, in extremes, can cause a wonky period schedule.
There's all kinds of reasons for it that are nothing to be concerned about. But, if any of these things are factors for you (as mentioned above), then I suggest that you talk it over with a professional that you feel comfortable talking to and if you feel comfortable talking with your parents or another family member, please do so. If not....we are here to talk to too.