Mirena for 2 years and 2 missed periods ??

I’ve had the mirena in since i was 16 and my period was irregular and after the first year became regular and consistent. I used to have extremely heavy periods so my regular period with my iud was about 6-7 days and regular flow. I am now 18 and on my second year and I have missed my last period and my current period was supposed to come today but it has not. I have not had sex with my boyfriend since before my last full period so I was pretty sure I was not pregnant. Took a pregnancy test today and came back negative and will be taking another tomorrow if my period doesn’t show. If anyone knows why I have suddenly missed periods after a very regular cycle please let me know! I have heard lots of stories of failed iuds and my cousin actually experienced an ecoptic pregnancy so I am just a little worried! I have also experienced a lot of sudden nausea that I assumed was from my acid reflux but I have also just got new stretch marks on my boobs and now that I am late for another period I am worried. My boyfriend and I have unprotected sex but haven’t since before my last period so idk how I could be.