Hi,
Welcome to the ehealthforum and I am really glad to help you out. Mirena is notorious for causing pelvic inflammatory disease and intrauterine adhesions. Pelvic inflammatory disease is an infection of the uterus, fallopian tubes or ovaries. It occurs when bacteria move upward from a woman's vagina or cervix to her uterus or fallopian tubes. Intrauterine adhesions can cause abdominal cramps and discomfort in the lower abdomen.
I sincerely advise you to consult a gynecologist and get cervical swabs and pelvic ultrasound done to find out whether PID is responsible for your symptoms. The gastrointestinal causes for such symptoms also have to be ruled out.
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.