I always thought I was pg when on Mirena too. I took a home pg test to make sure more than once. If you call your physician they will ask you to do the same thing. You have such a small chance of being pregnant the physician doesn't see a reason to see you unless you are. I gained quite a bit of weight in stomach on mirena and my OB told me it was due to the mirena and if I wanted to lose the weight I should take the mirena out. Hope this helps, and good luck.
you should see your doctor as its hard to tell