Hmm...
I'm not sure. I know I have heard about that kind of thing happening to women as they get ready to O. They say that when the egg "bursts" through, sometimes a bit of blood can pass with it.
I'm a bit hesitant to say it's O though, because of your CM. You haven't documented any fertile CM yet this cycle. I see in previous charts you have gotten both Watery & EWCM, so I'm just not quite sure.
I'd say to keep BD'ing just to cover your bases... you never know... it could be a

egg tryin' to Ninja it's way out without you knowing!!