mirena

I have had the mirena in for about 6 months now. The first 4 months were fine. regular periods no cramping or pain. However the last few months i have noticed my period has lasted more than 7 days and the color has changed to a very dark color. during this last week i started having cramps after my period was over. I dont know if it has fallen out or if i could possibly be pregnant. Someone please help!!!!