Mirena

I recently switched from Progestin only pill to the Mirena IUD and I also have been using a different period tracking app and it tells me I have a high chance of pregnancy today but my question is, doesn’t the mirena basically stop ovulation like the Progestin only pill? Also should I use condoms/other birth control around the time it says I have a chance of pregnancy, or should I be fine without? I had the Mirena inserted Nov. 12, 2018