I had mirena for about 2 months after I had my son. It was ok at first, I had some slight discomfort, occasional bleeding, light cramping. This was manageable and not so bad. I started getting infections frequently which involved my skin feeling very dry and itchy. I developed a lot of discharge that had a very unappealing scent and I had alot of burning sensations.
I thought I had a yeast infection originally and after using an over the counter medication my symptoms were alleviated but for only two days. They came right back. They then went away for a week and came back again. I was extremely frustrated because my doctor had all but promised that there would be no problems.
My frustration only worsened as my symptoms became much more uncomfortable. I couldn't even have intercourse with my husband because I was so tender and raw. It was awful.
My husband became worried and I was very upset. I was worried I had something seriously wrong and began doing research about these symptoms. It turns out, if you search you will find tons of forums full of women over a very large span of time all reporting symptoms like these. Many had problems much worse than mine. I have no idea why these aren't reported by doctors and I'm sure that Bayer, who makes Mirena, does not want to report it for their own reason.
I strongly strongly advise against using Mirena. Vaginal infections can be extremely frequent and will not go away for a long term period. I was absolutely miserable. The only reason I stress this so much is that I found so so so many instances of this. The warnings I read were much more extreme. You can use google and look it up.
I ended up having it removed and my symptoms all were relieved within a week. I will never use it again.