It is normal to experience some irregular bleeding after going off the
minipill as your body adjusts to the new hormonal milieu.
One option is to wait until after
tevilah as you suggested, as it allows you to take precautions against becoming
niddah from any staining. See our
article on stains for more details. However, should you experience an actual flow of blood (comparable to a period), you would become
niddah. This is a realistic possibility, and given your anxiety about further bleeding, that may not be the best time to stop the minipill.
Therefore, a better option might be to stop a few days before you expect your next period. This way the withdrawal bleeding will likely coincide with your period, and at most will add a few extra days to the bleeding before you can start your
clean days.
In any case, it is important to remember that your cycles may be a bit off for a few months after going off the minipill, so once you become
tehorah, you should be careful with the precautions against becoming
niddah from staining.
Please feel free to get back to us with any further questions.
B’Hatzlacha!