Hi!
You may want to consider getting checked to rule out infection of the uterus. If you were my patient, I would probably also do a transvaginal ultrasound to double check to be sure that the Mirena is properly positioned. If eveything turned out OK, I would give you a prescription for Anaprox DS 550mg twice daily, and have you take it at the first sign of pain, until the cramping is gone.
Good luck!
Dr B