What are causes of having irregular periods? does it mean i am less likely to conceive a child once i get older? im 16yrs and my periods change often.

Consult gyn: There are many different reasons for irregular periods. At 16yo, not unusual to have irregular periods as body/brain get adjusted to the maturing process. 2-3 years from onset of menses (menarche), menstrual cycle often becomes regular as normal ovulatory cycles occur. However, if ovulatory cycles persist or if irregular periods are bothersome, consult with gyn for evaluation and treatment.