I am a 16 year old girl and my period has been irregular and now it has came and hasnt stopped. it is day 10. it has been really heavy but now light?

That's not normal: Irregular cycles are very common in adolescents. Any period lasting more than 7 days is abnormal. Any chance you may be pregnant? If you have had unprotected sex, consider a home preg test. I assume you are not. There are a variety of ways to regulate your periods that are all very safe. Prolonged cycles may cause anemia and fatigue. I recommend a MD visit to check your blood work and start meds.

Common: I would not worry now. Unless you think you could be pregnant i would wait and see. sometimes a single period can be very long or abnormal. if it becomes a pattern then you would need to be evaluated for common hormone problems