What Causes Vaginal Bleeding And Abdominal Pain?

i am bleeding bad from my vagina its not clotty it started bright and now is dark...im dizzy have abdominal pain frequent bowel movements headache im not pregnet tht i know of my period is supposed to come in a week and i havnt missed a single birth control pill idk wats goin on but im sick to my tummy and all the bblood is freakin me out