I would suggest seeking additional treatment just to rule out that you do not have an underlying health issue. This is because often a doctor will treat the symptoms but not the actual problem with the Pill.
The Pill cannot not treat the underlying medical condition alone & alone as a course of treatment it will only mask it. Which could mean you don’t get treatment for something that you need. This could lead to later complications. You need to address what is causing the pain, extreme pain indicates you might have an underlying health condition. If your doctor hasn’t done additional tests before just giving you the Pill this is very important. Get a second opinion (see if you can get into an NFP doctor) make sure they do testing to rule out other health problems like poly-cystic ovarian syndrom (PCOS) or endometriosis (ENDO) for example.
It may turn out that hormones are part of the course of treatment & in that case it would be legit as pp wrote (it falls under the double principle effect) but you also don’t want to miss anything that could also help you feel better, live a healthier life overall & keep your future fertility healthy.
I have been there (I use to cry for days when I would have my period & bleed very heavily), please get a second opinion. It’s a real lifesaver to be able to feel more normal in your own body and to know you have done the best & healthiest overall course of treatment at the same time!
BTW–That’s wonderful to read that your BF is thinking about conversion to the Catholic Church & that you 2 are keeping your faith center in your relationship! You won’t regret it!! Many prayers for him as he makes the journey & for you as you move ahead in your future :gopray2: