MRCP2-1964

A 28-year-old female presents with a complaint of passing bright red blood per rectum. She has observed blood mixed with stool, mostly in the pan and on the paper. Additionally, she experiences bloating, alternating diarrhoea and constipation with some urgency and tenesmus. This problem has been intermittent for the past five months, and she reports no systemic symptoms. Her weight is stable, and she is currently taking senna and the oral contraceptive pill. What is the probable reason for her rectal bleeding?