Hi,
Welcome to ehealthforum,
The symptoms that you describe could be attributed to Mirena use or even pregnancy. It is difficult to comment on exact cause without examining you and going ahead with the further evaluation. If you suspect chances of pregnancy you should consider visiting your doctor/gynecologist for examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). If pregnancy gets ruled out, further evaluation would be needed to look for the underlying cause for the symptoms that you describe. Treatment as needed (based on examination findings and investigations results) would be started to help you. Take adequate rest. Drink plenty of water. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Maintain healthy diet and lifestyle.
Take care.