Mirena IUD after 3 years

Ive had the mirena iud for 3 years now, my periods before getting it put in was only 3 days but now that I have it in they have been going anywhere between 9 to 12 days and here recently I have been having just brown come out and no blood but it is on one day and then off the next but will show back up 2 Days Later and this has been going on for almost 2 weeks now does anybody know what this is?? Or is my iud maybe stopping my periods finally?