Typically, a woman’s fertile window extends for twenty-four hours past ovulation. Based on what you write, it still should be possible for you to conceive. However, you may wish to consult a fertility specialist at this stage to evaluate this and other potentially relevant factors.
On a halachic level, the hefsek taharah and bedikot need not be entirely clear. Light brown (lighter than coffee with milk), with no hint of a reddish tint, is an acceptable color. Questionable bedikot or stains (such as darker browns, or browns that might be reddish) are best brought for evaluation rather than assumed to push off the clean days. Please see our article “Ovulating Before Immersion” for more information, and please get back to us with any further questions.
If the situation persists, you may also find it helpful to consult a Yoetzet Halacha Fertility Counselor. (This is a free service, details here.)
This response was updated on 17 November, 2020.