The goal of this pilot trial is to learn if a novel non-hormonal treatment, metformin hydrochloride, works to treat pelvic pain in young women with endometriosis. The main questions it aims to answer are: * Is metformin superior to placebo in alleviating pain symptoms in young women with endometriosis? * Does metformin alter systemic inflammatory markers over 6 months in young women with endometriosis? Researchers will compare metformin to a placebo (a look-alike substance that contains no drug) to see if metformin works to treat pelvic pain. Participants will: * Take drug metformin or a placebo every day for 6 months * Visit the clinic three times: once at baseline (pre-treatment), once at 3 months, and once at 6 months * Keep a daily symptom diary to track pain, bleeding, and usage of any pain medications