I was almost at four months before I realized something was wrong. I am in a new relationship and thought wow, maybe my new sex life is giving me a UTI, so I went and got tested because something wasn't right. Burning at the end of urination, lower back soreness, frequency to go and getting nothing. Totally uncomfortable. I couldn't believe after a week that I wasn't getting a positive result on the UTI test. There was also a lost sex drive almost right away. I thought I could just "power through that" as we women sometimes do. After finding this site yesterday afternoon I was identifying with too many of the symptoms posted here. I went this morning to have it removed. When I talked to my doctor about it she read as if from a script. Telling me none of my symptoms have been related to Mirena. She even went so far as to say maybe I did have bladder issues that were being masked by the shot. Ten years on the shot, and no issues. Four months on Mirena and I couldn't take it anymore.
What a relief to get it out, and thanks for sharing on here. I was surprised it developed after four months, but "everyone is different". I don't have any children and thought this was a good method for me. It wasn't, and that's ok.