help.

Stormi
I should have started my period on the 10th, well on the 17th I thought I started when I got up for work and wipped and noticed blood. Well it's not normal to me. I have a pretty regular period and this is very light spotting. I took a test on the 17th and on the 19th  and they both said negative. I do have an IUD. Could I just be over thinking and freaking out ? I don't know what to do.