Are there any specific symptoms you get while pregnant and on the mirena IUD?

The spotting and the missing period may be the IUD. A lot of women experience breakthrough bleeding and abnormal periods while using an IUD. You should go see the doctor and see what they think, they will do a pregnancy test just to be sure. Also if you are pregnant your doctor will have to make the decision to try and remove the IUD and risk a miscarriage or leave it in and hope the baby pushes it up against the uterus wall. It can cause some problems if left in while pregnant. Hope everything works out for you.