Irregular periods are often caused from not ovulating every month. This is common in the first year or two after you start your periods. Some months you may ovulate and other months you do not ovulate. The frequency of periods may vary with sports participation, stress, weight changes, or a hormone imbalance. One possible cause could be a common condition called PCOS (short for polycystic ovary syndrome). Take this quiz to see if you might have PCOS symptoms: http://youngwomenshealth.org/2015/02/03/pcos-quiz/
Since certain symptoms can be caused by many different health issues, remember to talk to your health care provider about your medical concerns.