I have been on my period for more than 3 months now. what could be wrong?

Vaginal bleeding: Any new, unusual, or unexplained vaginal bleeding requires medical evaluation. There are many possible causes, some of them serious. Not possible to even guess at the cause without a lot more information, like your age, other symptoms (pain, vaginal discharge), and others. But nobody on a forum like this can help anyway. You need to see a doctor in person, the sooner the better. Good luck.