Can be pregnancy, an ovarian cyst, P.C.O.S., early menopause, a significan weight gain or loss, stress, an STD, endometriosis, etc... There are A LOT of factors that can do this. I'd need more info before I can give a more detailed answer. You can contact me though messaging on here or privately at [email protected] In order to make it not go to junk mail, use the subject line and put something like PMS, or period help. I will try to help you privately if you prefer.