The pill won't mask functioning of other body systems. It simply provides a higher hormonal level. But it won't disrupt other body parts from actually working. The point is to treat the symptoms, and as long as everything has been checked for a more sinister cause then why wouldn't you want better symtpoms. You can further investigate while also treating the symtpoms and pain, and bleeding. One doesn't cancel out the other.
I recommend asking the GP to try the pill and/ or mirena coil can be amazing with heavy bleeding and pain. You might try different pills for a while. The mirena will may the uterus lining thinner, less bleeding, and less cramps), but with the pill, will treat symptoms. So definitely try that. Sometimes the progesterone only pill (mini-pill) can be better for some.
Also, ask your GP for mefenamic acid and/or naproxen (NSAIDs, which help a lot as they are anti-inflammatories and give pain relief). and tranexamic acid (helps reduce heavy bleeding) - you need to start taking it days before your period starts so that it can work at the best capacity. The same is true with ibuprofen and/or paracetamol. Start taking it 3/4 days before, and it will be much better.
Also, you can try some meds to try and shrink the fibroids. Progesterone through the mirena coil or pill, GnRH meds which cause a temporary, medically induced menopause to shrink fibroids. So, for example, linzagolix or injections like goserelin) or nasal sprays.
FYI GnRH meds can cause a temporary medical menopause as well. You can however get add-back therapy (so HRT) with low-dose estrogen to help manage side effects and allow you to take the GnRH meds for 6-12 months. Often its not taken for longer due to risks for bone health etc. Or you can get vaginal progesterone instead like the pessary or the gel.
The mirena and the pill essentially mimick the luteal phase, as your fibroids aren't that big, if you get it inserted right it could help - so make sure you take paracetamol and ibuprofen 1h before and also insert licodaine into your cervix and also numbing gel/spray. Call them before/write on any like booking or online forms and make sure they give you all of that and have it ready. Just as sometimes they don't offer them but have them available. It depends on the place but I know it's becoming more common now, as it should be. So during a menstrual cycle, progesterone is released later on (luteal phase) - it basically tells the hypothalamus and pituitary glands, stop now you've done your job (which is thickening the uterus lining, estrogen's job), let's not go overboard and progesterone maintains the uterus lining (whereas after your period, estrogen stimulates it to grow more). Essentially, the hypothalamus, or pituitary glands, at that point stop producing FSH, LH - that means that less estrogen is produced. Because when LH and FSH are released, it triggers a follow-up of estrogen.
The mirena uses synthetic progesterone to thin the uterus lining and help to shrink things like fibroids. It also suppresses estrogen secretion to hopefully stop more growth of the uterus lining (helpful for periods as there should be less bleeding and cramps). So, mirena coil mimics the luteal phase. I'd really recommend based on my personal experience, but not for fibroids in my case.