Miscarriage? Or just the plan b?

My period is so heavy i soak through a ultra absorbant tampon in 20 mins and already leaking through to the pad which soaks in 5 mins .
I took plan b, and got my period VERY early, 2 weeks early. And now im having pains and sucha heavy period, i cant go to sleep without drenching the entire bed in blood? what do i do !