Glycemic Regulation as Endometriosis Adjunct Treatment

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

Inclusion Criteria: * Female with surgically confirmed endometriosis, determined at laparoscopy * Current use for at least 2 months duration of a consistent hormonal therapy for endometriosis (either combination hormonal contraceptives or progestin-only therapy) * Current pelvic pain (score ≥ 3 on Visual Analog Scale) that has been present for at least 2 months prior to enrollment * Age 15 years to 35 years and premenopausal * Willingness to comply with visit schedule and protocol Exclusion Criteria: * Pre-menarche or post-menopause * Diagnosis of Type 1 or Type 2 Diabetes Mellitus * Severe renal dysfunction (creatinine \>1.4 mg/dL or eGFR below 45 mL/minute/1.73 m2 * History of lactic acidosis or diabetic ketoacidosis * ALT or AST \> 2.5 times the upper limit of normal * Significant mental or chronic systemic illness that might confound pain assessment or the inability to complete the study * Current/planning pregnancy or breastfeeding * Inability to read English