I didn't have the Mirena, but another IUD, and had horrible problems with it, to the extent that they thought it would prevent me from having more kids. It tore me and I bled so bad and originally they couldn't figure out what was wrong. I ended up in the ER because I couldn't even walk and was bleeding so bad, they talked about doing a blood transfusion.
After talking with my Dr. (a different one put the IUD in) he advised me that he is against IUD's and will not put them in, if one of his patients wants them, he refers them to another Dr. in his office for that. I wish I had spoken to him about it before I had gotten mine, because I never would have done it.