I had mine removed a week ago Friday and started the worst period of my life on Sunday. I too had some very large clots and by day five was getting very worried. Friday morning, I passed a pretty big one and that was the end of my period.
I can't help thinking that it sounds like the first period I would have after I had given birth. It would be huge clots and very painful, but my doctor told me it was just the left over stuff coming away from the lining of the uterus. I know it sounds awful and it's pretty scary to see it coming out of your body, but I would probably take it as a good sign that things are returning to normal.