Can’t feel IUD strings

So I’ve had the Liletta iud for almost two months now. I went back for a follow up after having it inserted and all was well. But as of recently, I’ve gone to check the strings and could not feel them. I immediately got into the doctor and she also could not find them so I’m having a sonogram tomorrow to locate it. Has anyone experienced this before and had a positive outcome? Could the strings just be curled? What are the chances it’s moved completely? I’m so nervous now :(