IUD use and possible pregnancy?

I have three kiddos so I know what to expect with pregnancy, but currently I am using an IUD. It has definitely become displaced (per urgent care), and apparently that isn't a priority for any gyno, I can't be seen until the 28th of Dec.
Problem is - I think I could be pregnant. Just a feeling, you know. I took a HPT (8 days ago) and it was negative. But now, I'm also 3 days late for my period. 
I just don't know what to do, if I am and don't go in right away it could be dangerous. If I'm not and go in I look like a loon.