possible pregnancy?

I've had the copper IUD since December and my period has NEVER been regular, but 3 weeks ago I had sex and we did not use any other protection, however he did pull out. Then two weeks ago I was supposed to get my period and I had about a week of light spotting instead. The spotting has stopped and now my period is still late (14 days) it's been late before but I'm worried about the fact that I've had sex. What are the chances I could be pregnant? And has anyone had this happen to them?