J.S.
I've had the Mirena twice now. The first time I spotted for three days or so. The second time was to replace the first one, and I spotted for about the same time.
The bleeding from insertion shouldn't last very long, not more than a few days. I would say that if it's been a week and shows no sign of stopping and is heavy like a period, then you really need to call your OB.
If it's time to have your period, you could very well still be getting your period. Not everyone stops getting their period on Mirena.
In any case, call your OB about your concerns.