Thanks for your comments. If AF doesn't rear her ugly head by Monday, I'll call my doctor. I'm a firm believer in timing and if this isn't our month, then it isn't our month. We'll just keep trying.. :)
It could be pregnancy and just too early for a positive test. It could also be breakthrough bleeding/spotting which is not uncommon, even if you have never had it before. That can be due from anything from a mild hormonal imbalance to rough sex...and a million other things. Typically it's nothing to be concerned about though. Just annoying. I personally never experienced implantation bleeding and it's not super common, although it certainly happens. I know the wait is awful, but at this point it's really all you can do. Once pregnancy has been confirmed or ruled out, your Dr. can do some tests if necessary to try to find out what caused the bleeding. Good luck to you, and SSBD.