What Causes Stomach Cramps While Using Mirena Coil?

I have had Mirena inserted for about a month now and for the past two weeks, I have been expierencing severe cramps. But it doesn't feel like regular period cramps. These cramps just come out no where. It's comes and goes throughout the day. and when it comes, it hits me hard. I can't walk...I just want to curl up! what can this be?