It makes me so sad that this teaching hasn’t got through, judging by the frequent threads on the subject. Not at all getting at you, OP! Somebody is failing you and all the girls who suffer, and it shouldn’t be happening. I am really sorry for you.
I can understand a married woman wanting to check, but how can it be that any unmarried girl goes through such worry unnecessarily? I mean, evidently somewhere along the line the message 'no artificial birth control ’ seems to have been successfully transmitted, but the other message in the encyclical, ‘the Church isn’t a monster and so doesn’t oppose prescribed medicine to alleviate pain’ hasn’t?
This should be covered in all Catholic schools/colleges as a minimum, surely, even if not addressed from the pulpit.
I can think of many reasons why some Catholics assume “birth control pills” are never licit for any use.
One is an understandable over-reaction to the dominant cultural narrative, that not only is “birth control” licit, anyone who doesn’t use them must be ignorant at best, irresponsible at worst.
Another is a reaction to the fact that many Catholic women take “birth control pills” ostensibly for some medical reason, but actually see this as a loophole to Church teaching they can exploit, and their true reason for using the Pill is indeed birth control. I can think of more than one CAF poster who freely admits that “I’m so glad I have a medical reason to use ABC, I don’t have to worry about NFP not working!” They seem to have a legalist approach to morality.
Another is a distrust of medical professionals and the pharmaceutical industry. If I had a nickel for every time I have read a CAF post that claims “all birth control pills do is cover up the symptoms, they don’t do anything to cure the disease” I could go to Starbucks free every day, at least for a week.

. (Yet, one could say the same about blood pressure pills, yet no one has ever questioned the morality of taking them.)
(And if I got a nickel for every time I read a CAF post that claims NaPro technology is a guaranteed cure-all for all gynecological problems, and seems to assume Napro is accessible and affordable to all Catholics, I could probably go to Starbucks daily for two weeks.)
Another is the influence of American fundamentalist ideology. While Catholics find it absurd that, say, Baptists obsess about “Demon Rum” and ban alcohol, as if alcohol itself is somehow sinful just by existing, I have noticed that many of the very same Catholics somewhat inconsistently obsess about “Demon Birth Control Pills” and act as if the very existence of the medication is sinful.
All this being said, I realize there is some theological grey zone when it comes to sexually active people using medications that may have an actual “abortifacient” effect. However, that still doesn’t make non-abortifacient uses of the medication illicit. Methotrexate comes to mind. It can be used as an “abortion pill” but it’s much more common to use it to treat arthritis. I doubt an 80 year old long-postmenopausal woman would be sinning by taking methotrexate.