Ectopic cervix (also called ectropion or cervical erosion) often leads to post-coital bleeding. Bleeding likely resulting from ectropion, at a time when the menstrual period is clearly not expected, does not make a woman niddah, even in conjunction with relations. Although bleeding following relations sometimes leads to a requirement to perform bedikot in conjunction with the next act of relations, that halachah does not apply here.
We do suggest that you be particularly cautious about not having relations around the time of your anticipated period. At non-veset times, you may attribute bleeding after relations to your condition.
You may well wish to seek a second opinion about treatment options, which are sometimes effective in reducing bleeding.