Hello,
Chances of pregnancy are less in your case and the symptoms can be due to hormonal imbalance due to the Mirena IUD. However to confirm the status of pregnancy, I suggest you to get your serum HCG levels estimated since this is more specific than urine for pregnancy tests.
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.
Seeing your doctor is always a good idea when you don't feel like yourself.
Have you tried a home pregnancy test? You might get the answer you're looking for with one of these over-the-counter tests.