Firstly, consider a visit to an orthopaedic clinic, as low back pain and leg pain are common orthopaedic symptoms, while the left lower abdominal distension may be due to a painful sensation in the lower back radiating to the abdomen.
The diagnosis can be confirmed on admission with X-ray plain films, CT examinations and relevant laboratory tests. If there are no skeletal and muscular lesions, further investigations will then be directed by the doctor.