What could be causing my period to be 9 days early?

Uncertain: Reasons for an early period can include endometriosis, emergency contraceptives, changes in hormones, polycystic ovarian syndrome, chemotherapy for uterine cancer, perimenopause, eating disorders, intense dieting (especially w high carb diet), marked weight gain, significant over-exercising* anovulatory periods. May be it is break through bleeding and not your period.