Hi, Thanks for posting in HCM. I understand your concern. Plan B is an emergency contraceptive pill which should be taken within 72 hours of unprotected sex. It prevents pregnancy by causing break through bleeding within 3 weeks from the day of intake of the pill. Hence, kindly wait for it to happen. In case you don t get bleeding in the form of periods within 3 weeks, you need to seek medical attention immediately. Sometimes, you might experience brownish vaginal discharge prior to periods, which could be due to shedding of lining of endometrium or cervical mucosal erosion or remnant tissues of previous menstrual period. Experiencing backache during or before periods is a pre-menstrual symptom and symptomatic treatment needs to be taken in the form of analgesics along with calcium and iron supplementation. Hope the information provided would be helpful. All the best.