A friend of mine has a Mirena and is about to start a law suit against the hospital who inserted it because they didn't do it properly and when she was in the stirrups they moved her leg too far and tore all the cartlidge in her hip. She's had one lot of surgery to try to fix the hip but it's beyond repair.
She's had 3 years of problems every since getting the Mirena inserted. She also had similar problems during pregnancy to what you have. Please be careful and do all your research first.