Your symptoms, itching, watery discharge, and lower back pain, suggest a vaginal infection, such as a yeast infection or bacterial vaginosis. The presence of lower back pain is important, as it can sometimes signal a deeper pelvic infection or a urinary tract infection. Because yeast infections require antifungals (like fluconazole) while bacterial infections require antibiotics (like metronidazole), you need an accurate diagnosis. I strongly advise against self-medicating with over-the-counter products. Please see a healthcare provider for a physical exam and a swab test so they can prescribe the correct targeted medication to resolve your symptoms safely.