It can be due to stress or some other health issue. Get the help of your family doctor or Gynecologist near you. They will suggest you what exactly you have to do for your regular period. Or you can also consult online get all your answers.
Various Reason is lead to irregular periods at this age since. You need to consult for this condition to the good gynecologist, who can help you in this situation. Don't take too much stress just relax and consult a doctor. since some girl have normal periods at this age and some not due to various factor diet, stress and other factor are there: