Miscarriage or really bad period?

Really bad period or miscarriage?

I'm having really really bad back pain in the middle/lower area of my back. Last night I woke up to sharp pains in my stomach and side. Not cramps in my pelvic area. And I just used the bathroom and at the bottom of the toilet was a pretty big clot (2in by 3-4in). And my blood would not absorb in to a tampon very much yesterday it was very clotty. Now today is super heavy and dark red blood. I feel very sleepy, lightheaded, and nauseated.