What Causes Severe Vaginal Bleeding And Cramps?

im about 3 weeks late from my regular menstral cycle and i spotted a few days ago and as of last night i have had constant vaginal bleeding and extremely horrible pains, i think there may be clots in the blookd because some of it is thick and not liquid like but i dont know if its my period just hurts and im bleeding so much b/c im late or if i should go to the hospital