Period strange on Mirena

I got a mirena in September 2013, after the first adjustment, no periods, that was okay with me.

But then about a year in I started to get light periods regularly. When to the doctor to see if anything was up- it was still in and positioned correctly.

Then regular periods stopped, and brown discharge (which is old period blood) spotting throughout the month- kinda gross.

Now no period again (just spotting seemingly whenever).

Has anyone else's period seemed to just be a bit crazy on mirena?