hi, the chemical in mirena only lasts around 5 years, although it is not going to be exactly 5 years to the day - for some it may be used up sooner or later than others, so it is possible that the chemical has diminished in your body, as you have had the mirena for a little over the 5 years already and obviously that would make you unprotected as far as pregnancy is concerned. I would get another test done at the doctor's surgery, and when you get the mirena out, don't get another one put in until you know for sure that you are not pregnant - i am sure that if there is any query over pregnancy then the doctor would not offer you another mirena yet anyway. If it turns out that you are not pregnant, then it would likely be your hormones telling you they are not too happy - they fluctuate all the time anyway and obviously the mirena is not natural and can have serious effects on how your own body deals with and produces its own natural hormones - this accounts for the terrible and debilitating side effects that some of us get. people can get side effects on mirena (irregular or no periods at all being just one of those many effects) even towards the end of the 5 years, and some don't get them until the next mirena is put in - it is difficult to know if in those cases, it is just that their own hormones have got to the end of their tether, so to speak, or if the new mirena, being a different batch from the older one, is releasing too much chemical either due to being faulty or perhaps because the manufacturers have changed the amount in there slightly. All we know is, through our own experiences on here, that one can never relax with mirena, because side effects can start at any time - even when it comes out, as the body tries to rebalance itself properly again.
I guess the best thing you can do right now is hold on tight, get the mirena out, get another pregnancy test done and then see where you stand. sorry that is probably not a lot of help but until we know what we are dealing with it is difficult to suggest any other course of action...good luck for the test and for removal and do post back to let us know what the results are and how you feel. xx