You may want to call your doctor about this and get tested or have pregnancy ruled out. Let us know how everything goes.
Hello,
Pregnancy is possible with Mirena IUD. These can be the symptoms of pregnancy. If you miss your periods then you can test 1 week- 10 days after you miss your periods or you can test for pregnancy by a highly sensitive pregnancy test 10 days post ovulation with a sensitive ( 20 - 25 mIU ) pregnancy test. Also I would suggest you to get your serum HCG levels estimated since this is more specific than urine for pregnancy tests. The HCG (it is a hormone) levels rise only in pregnancy and its presence will confirm the status of your pregnancy.
If serum HCG test comes positive then you will have to get Mirena IUD taken out immediately.
I hope it helps. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.