Why is my Mirena suddenly being weird?

I've had my Mirena since November- so about five months- and it's been a pretty good experience. My periods have been coming on schedule, although they've all differed in how long they last. However, after this last period, I haven't stopped spotting. And I mean like really LIGHT spotting- maybe once or twice a day- with no cramping or anything. I'm not tooooo worried since it's an IUD and I'm not really expecting it to last, but I was wondering if this has happened to anybody else? Thinking of consulting my OBGYN if it doesn't stop after my next period.