It’s actually very common to have irregular periods during the first year or two (after your period starts), but after that your periods should become more predictable. Irregular periods can also be caused from your hormones not being in balance, from low weight, being super physically active, pregnancy, and different kinds of medicine can also affect your menstrual cycles. Talk to your health care provider and be sure to tell him/her about all of the medicines you take, including over-the-counter herbs, diet pills, and birth control pills.