IUD, Implantation?!? Help!

A
I had sex on cycle day ten, it's now day 14 and I'm spotting. This rare for me to spot, I've had my Iud for a year and it has never failed. My periods are always regular. I'm wondering if this could be implantation spotting? My Iud is in place I can feel my strings. There is quite a bit of mucous along with blood. 
My questions are could it be implantation? When can I take a test? Should I call my doctor? I could use some advise