Paranoid on IUD

I know Mirena is supposed to be very effective but I’m seeing a lot of people got pregnant on it. I guess I don’t have a question I’m just paranoid. My husband and I decided we weren’t ready for another anytime soon so I got the IUD. My strings are too short to feel. My doctor said she cut them short when she inserted it. I felt them barely sticking out of my cervix after a few days. Then never felt them again. I need to go get checked since I’ve had the mirena little over a month. I’m not having any pains or anything just spotting this whole month since I just got it inserted maybe 6 weeks ago.