Possible Pregnancy While on Mirena

I currently have the Mirena IUD. I had it placed after I had my son and have had it for 4 years and 9 months. Every month, of every year I got my period. Never missed one. It may have come a day or two late but it ALWAYS came. Last month my period came late and lasted  3 days opposed to its normal 5+. This month my period is 10 days late with no sign, symptom or inclination of a period. I've taken 2 preganancy test so far, both negative. However, my body feels off, like a chemical imbalance. I reached out to my OB, I'm scheduled for blood work December 7th to check for pregnancy. I plan to keep testing until then. Any body ever gone through anything similar?