Mazal tov on your upcoming wedding!
It is unclear from your description of breakthrough bleeding what you actually experienced.
If you experienced staining on colored underwear, or found stains smaller than a gris on your white underwear, you may disregard the stains. If you saw blood on toilet paper, and waited at least a few seconds between urinating and wiping, you are also not considered niddah. If you are still counting the shivah neki’im before the wedding, you should ask a specific question to a halachic authority before continuing bedikot. (In general, the number of bedikot should be reduced in this situation, but a bedikah on the final clean day is generally required.)
If you found staining that was not bright red on a bedikah, or such stains larger than a gris (the size of a US dime) on white underwear, then you should have them evaluated by a halachic authority, since not all shades would render you niddah. If you found blood on toilet paper immediately after urinating, you should also ask a question, even if you did not save the toilet paper. In these situations, you should also ask about the possibility of reducing bedikot.
If you experienced an actual flow, or red staining of any size on a bedikah, or red stains larger than a gris on white underwear, then the situation is more problematic. However, we recommend that a kallah always ask a specific halachic question before considering herself niddah before the wedding. There is still a chance that a halachic authority could find a leniency that would let you avoid a chupat niddah.
Since these questions are time-sensitive, we recommend contacting a local rabbbi or yoetzet with any follow-up questions, or calling our telephone hotline.
Even if you were rendered niddah, it is important to remember that even with the best of planning, problems sometimes arise. A couple in these circumstances should remember that marriage is meant to last forever, and a few difficult weeks in the beginning will not overshadow a lifetime of happiness. You should be in contact with your mesader kiddushin to arrange the details of the wedding in a discreet manner.
We wish you much hatzlacha as well as a wedding full of simcha!
This response was updated on 8 February, 2024.