My IUD has moved!

Hi girls, so in the last 6 months I have been getting really bad pains in my uterus. I had an ultrasound and found out I had a cyst in my right ovary measuring 47ml (my left measuring at 4ml). 3 months later I had another ultrasound that showed the cyst in my right ovary popped and I now have one in my left ovary only measuring at 27ml and that my IUD has moved closer to the left. My dr assured me that the IUD moving slightly won’t affect me and that I won’t get pregnant. My question is, how much does the IUD need to move for it to become ineffective? I know I should trust my dr but I’m paranoid