Why does my period keep coming early?

Hormone inbalance. Your hormones are not working the way they should which is very common at your age. I always will do an exam, do blood work and an ultrasound. Then i can determine what needs to be done to regulate your periods. Usually it is nothing serious, and can be treated. Also at your age once any serious problems which are uncommon are ruled out I do endometrial ablation in office which stops the bleeding.