What Causes Brown Spotting With Abdominal Cramps While On Mirena Coil?

I have the mirena IUD. I had it put in june 26, 2009. I got my period for the months of july and august. Since then i havent gotten it and have had no problems with the IUD. In march i started spotting and cramping. In march i would have some cramping almost everyday. Then it went away. A couple of weeks ago i was driving down the road and felt something in my stomach, like a baby kicking. I went to the doctors but the test was negative, and my doctor said it was an abdomen muscle spasm. well yesterday i had the same kind of movement in my stomach but not inthe same spot, and then last niht i was having brown spotting and then today it has been pinkish red, and im having cramps. what are the chances im pregnant?