MISSING IUD?!?

Megan
Help!! Today I had my doctor try to check the strings of my Mirena IUD cause I've been nauseous for over two weeks, all day and all night (no vomiting) and she could NOT find the strings. 
I got my IUD in August, doc said the strings were cut short. Is it possible it's there but the strings are incredibly short?? I didn't go to a gyno so maybe she didn't know what she was doing as much (idk)
Getting an ultrasound Monday. Might do it sooner. Can't live with the fear of potentially being pregnant (side note I took a test two days ago and got a negative). I also recently had a period (aka 1 day ago it ended)