If the bleeding is an actual flow of blood (comparable to a period) it would make you niddah. If this is the case please speak to your doctor about hormonal treatment for this bleeding.
Most likely the ovulation bleeding you describe is staining, which does not always make a woman niddah. Stains found on colored underwear, disposable pantyliners, or on toilet paper (not immediately after urinating) may be disregarded. Please see our articles on stains and toilet paper for more details and get back to us with any further questions.
B'hatzlacha!