What are the causes of a heavy period and how can i have a lighter period i started yesterday and today it kept bleeding and didnt stop and it got to the point where i have to stay sitting down?

You are not clear if this is a recurring problem or a single episode. If you usually have heavy periods then a birth control pill is often used to manage them. Episodes of heavy bleeding in younger women are often associated with a pregnancy/miscarriage. In any case a consultation with your gynecologist would be appropriate.

Your doctor can prescribe pills that would limit your period to once a year. Take oral iron and multivitamins to prevent anemia from blood loss.