Mirena and Periods

I've had mirena since 2016. I've never missed a period and my cycle is usually a lighter to medium flow. I should be coming off my period today, but it hasn't even started. I took a pregnancy test (I had sex with my husband on the 3rd) and it showed negative. It's just really odd to me that I haven't started my period. I know periods can change with mirena, but it's usually around the 1 year mark from what I was told. I've had this birth control for 3.5 years and this is the first time my period hasn't stuck to my normal cycle. I have another test I'm talking this weekend since that'll be the 2 week mark since the last time he finished in me, but I'm curious to know if anyone else has ever experienced this?