Late Period/IUD Concerns

So I've had my IUD (Skyla) since July of 2015 and every since I got it out in, I've skipped my period every other month. I'm four day late this month and I was expecting to have it this month. My boyfriend and I are extremely careful. Always use condoms as well as him pulling out plus the IUD. I'm starting to get a little worried though. But really what are the chances of me being pregnant? Any advice?