Effectiveness of Ambulatory Transcutaneous Tibial Nerve Stimulation for Overactive Bladder

The goal of this clinical trial is to learn if using a portable nerve stimulation (TENS) device during daily life works to reduce overactive bladder (OAB) symptoms in adults aged 18 to 65. The main questions it aims to answer are: * Does using TENS at home during daily activities reduce the number of urgency episodes? * Does this approach improve bladder symptoms and quality of life as much as clinic-based treatment? Researchers will compare two ways of using TENS applied to the ankle area (tibial nerve stimulation): * Group 1 (Clinic-based): Participants will visit the clinic twice a week for 2 weeks and receive 30-minute TENS sessions. * Group 2 (Ambulatory): Participants will use a portable TENS device at home during their daily routine when they feel the urge to urinate, over a 2 week period. Both groups will use the same electrical settings (20 Hz frequency, 200 µs pulse width). Participants will: * Complete bladder symptom questionnaires before and after the study * Fill in a 3-day voiding diary to track how often they urinate, urgency episodes, and any leakage * Answer quality of life questions at the start and at 4 weeks