What Causes Constant Bleeding Post Medical Abortion?

I am 31 years old, my hight is 165cm and I weigh 51 kilos. Two days ago I finished the second part of my medicinal ebortion (2 pills of Cytotec given orally), and for the past two days I have had terrible cramps and maybe a little fiver (but no other side-effects). My question is: I'm bleeding constantly but have not passed any lumps, only tiny dark red clots from time to time... does it mean that the sac has not come out? And if not, can it still happen later? (Sorry for the bad English, it is not my mother tongue).