blood clots

Eva
Hey everyone,
I was wondering if anyone might be able to shed some light on a situation I'm having. 
I used to have the mirena iud and had really bad ovarian cysts. That was the only symptom I had other than a light period. I took it out because the cysts hurt. Shorts after I got pregnant and had an early term abortion and the iud placed in again. Now I have been having a period and clotting following my period. There is no blood, just clots (idk what it is). 
Does anyone know what could cause clotting after period ends?