Rhonda....
I am sooo just guessing here... but maybe this might make some sense?
You were showing + OPK just days before that. I would say chances are pretty good that it wasn't AF.... but just some form of spotting. Give it a couple days and then test again. I am thinking it was possibly implantation spotting!!!!

<fingers crossed>
I sooooo hope you Oed really late and this is it!
Good Luck....you deserve a bright pink BFP!