No period with Mirena IUD (maybe TMI)?

With my first IUD, my periods shortened from six days down to three and I would be like clockwork, always the same date every month and in the late afternoon. Then I got pregnant with it and had it removed. At my six week check up after having my second son, I had another IUD put in (that was 16 months ago). My periods with this IUD were really more like spotting instead of actual bleeding and were nowhere near as regular as they used to be with the first one. They would be a few days off here and there over the months and would last about 2 days. I should have gotten my period on Thanksgiving (but didn't) and took a test that day that came back negative. I took a second test (different brand) yesterday which also came back negative. I know not having a period is common with Mirena but for those who stopped getting them, how long did it take before you did? I thought that if I were going to stop getting my period, it would have happened closer to the time it was put in and not a year and a half later. I don't have any of the symptoms that I'm pregnant, but then again, I don't have any symptoms of getting my period either. I'll wait until the end of the week before testing again, but any experiences about not getting a period with Mirena would be appreciated. Thanks!