Good advice, I didn't think to throw that in!
As GA says, it's pretty normal. However, if you bleed a whole lot, or get dizzy and faint, or get feverish, go to the ER or at least the doctor. I was told to go in if I filled a maxipad in less than an hour, but in my case, I would "flood;" when lying down it was pretty normal, but when I would get up to go to the bathroom, a whole cereal-bowl full of blood would rush out. So I did go to the doctor, and finished the miscarriage in the hospital.
It is normal to bleed heavily and pass clots when miscarrying. The heavy bleeding, clots and cramps typically last anywhere from 1-3 days but can vary. You will likely bleed for longer than that tho, just not as heavily. I'm sorry you are having to experience this :(