M.R.
I am a test waster. I always tested even when I knew I couldn't be pregnant, I tested monthly when I was breastfeeding (even though I was on birth control, just not having periods), and then when we were trying for #3 I kept testing way too soon. I have never been on mirena, but on my last birth control prescription I had up to six weeks between periods, then periods that were horrible (sometimes two weeks long, heavy, miserable). It couldn't hurt to buy a test if you're able to, but again I don't know anything specific about mirena. I had crazy hormone issues with my last birth control, too. Good luck!