Having very heavy bleeding and cramping does sound like a miscarriage. When I went thru mine, it was like I was having the worst period of my life. I was in sooo much pain from the cramping and I passed a lot of blood and clots.
I'm very sorry that you've had to go through this. But go back to your doctor ...s/he will be able to confirm it with an ultrasound and blood tests (your hcg levels will drop).
You may have miscarried, it sounds like some symptoms of it, but when i was miscarrying the pains were sooo bad that i couldnt move, i was bleeding like no tomorrow and i was throwing up as well. I am so sorry you have to deal with this heartbreak. But like becky30 said go to your doctor
Oh, I'm sorry you're dealing with this scary situation. I don't think you can really know anything until you go back to your doctor and get another U/S. Keep us updated!