There is some research that says women can O twice in a cycle dpending on the moon cycles. Apparently a full moon can induce some women to ovulate again even if they've already O'd that month. That's why if you are following natural fertility management guidelines it is recomended that you abstain for a few days around the full moon each month. It would be interesting to check the full moon cycle against your suspected second O to see if it was actually a moon O.