When a woman omits the bedikah on onah beinonit, she remains tehorah but the couple may not have relations until she makes up the bedikah. So you still need perform a bedikah, even if some time has passed. If it comes out acceptable you will remain tehorah until you next experience a flow or if you find a stain that renders you niddah.

You are only required to calculate vesatot from a flow. This means that if you had performed a bedikah on your onah this month, even if you had become niddah from what you found on the cloth, you would not have been required to calculate any vesatot for next month. Therefore, next month you may take precautions against becoming niddah from any staining (by wearing colored underwear, waiting after urinating before wiping, and abstaining from intercourse while staining). You are not required to perform a bedikah (nor should you).

Please feel free to get back to us with any further questions.

B’Hatzlacha!