It's completely normal to lose your period after awhile if you have a Mirena. (After several months on the Mirena, I would have only light spotting every six weeks or so, never a normal period.) If the pregnancy tests have all been negative, then you are probably not pregnant. It sounds like you are experiencing side effects of Mirena messing up your hormones, which happened to a lot of women who have posted on this forum. My advice would be to have it removed and use another method of birth control, ideally something non-hormonal, and see if you feel any better. It can take months for your body to go back to normal, though.