IUD strings recoiled?

Sam

I got my skyla almost a month ago and went for my week 4 checkup. I have had zero problems after the first two days, other than my period being early (which she said is normal). Today she couldn't find the strings. I have to go next week for an ultrasound just to make sure it's in place. She didn't seem worried, but I have an anxiety disorder and I am a wreck! Anyone else experience something similar that can assuage this worry??!!