Mirena IUD and pregnancy

So I had my daughter last October and got the IUD immediately after having her (at my check up) and my periods became regular and always lasted 4-5 days. My last “period” was 2 days of spotting and one day of bleeding. The day I bled it was maybe for a few hours then nothing. Me and my boyfriend had sex that same day and 4 days following it. My period is now 12 days late and I’m freaking out. I have been tired more often, very emotional, frequent bathroom breaks, and have had more discharge than I usually do. Has anyone become pregnant while having this IUD? I took a test when I was 7 days late and it was negative.