IUD issues

So I'm freaking out a bit. My iud strings tend to disappear and reappear a lot depending what time of the month it is. Well, I went to the Ob the other day to get it removed as I'm ttc and she couldn't find the strings. The appointment was only 15 minutes long and she was unsuccessful. So she ordered an ultra sound to make sure it hasn't perforated the uterus, but that night when I got home I could feel the strings since she was trying to tease open the cervix (they have since disappeared again) my appointment isn't until the 27th for the ultra sound but I'm worried sick of it perforated my uterus, but I haven't had any pain and sometimes the strings are there. Has anyone else experienced this, and what are your thoughts? No pain or symptoms indicating perforation. (Sorry for the long post I've been sick to my stomach worrying, and crying everyday)