What the heck is going on?!

This was my first cycle of IUI. We went in on Jan 21 for the IUI and AF would normally be due tomorrow. But this entire last week (since about 7 days after the IUI) I've been spotting.

It's been mostly very light hardly noticible and mostly a rustly old blood look. It's been off and on all week, sometimes heavier than other times but never heavy enough to need a panty liner.

I've heard of implantation bleeding but I didn't think it was supposed to last this long. I typically spot a bit before AF but never like this. Is this possibly something caused by the IUI itself? Has anyone had any experiences with anything like this?