Late period while on mirena?

I've had mirena for nearly 3 years and have never missed a period and it's always started almost exactly on the same day every month. My period is over a week late and I've taken several pregnancy test that have all been negative. Has this happened to anyone else? I hope I'm not pregnant, I just got back from my honeymoon in New Orleans and spent most of my time on Burbon street! Eek