Hmmm, I was trying to find an answer in TCOYF and the only thing I could come up with is either you O'd then and it's midcycle bleeding or it's still your period.
Other than that it says to seek medical attention if bleeding occurs. This is what it says:
If however, the spotting lasts more than a couple days, is bright red, or you notice spotting at other timed in the cycle that do not coincide with ovulation or the approach of AF, it could be an indication of a problem requiring medical attention.
Is this normal for you, or is the first time you've noticed something like this? It could just be a fluke cycle.