What can cause pelvic pain?

Many reasons: Your pelvis has many organs in it;s vicinity. Uterus, tubes, ovaries, bowel, bladder and spine. Pathology in any of these can cause pain. Pelvic varicosities leading to pelvic congestion can cause pain too.

Pelvic pain: Pelvic pain in a young woman is commonly due to infection, cyst, endometriosis, bladder or bowel issues, or early pregnancy problems like ectopic.

Referred & spasm: Pelvic pain originates by referral or de novo. Referred pain derives from pelvic girdle joints, SIJ & symphysis pubis. Local tissues generate pain via bleeding such as Mittleschmerz, inflammation of infection, or smooth muscle spasm, as occurs in IBS; pain of which, in my experience, is sometimes misinterpreted as a factitious disorder called "endometriosis"; which lacks etiologic proof.