Question about IUD?

I'm 6 months postpartum and I have the IUD for birth control. I've been cramping extremely bad today and have a little spotting. Like a few tiny dots in my panties. I don't get a period, but it seems like every time at this time of the month I spot and cramp a bit. I'm nervous I'm pregnant, but anyways is this normal to cramp and spot with the IUD when you'd normally have a period?