I have a headache on my left side and a pain in my left leg.

Headache and leg pain on the left side are usually caused by cerebrovascular disease or cervical spondylosis. Suggestions: You can go to the neurology department or orthopedics department of the hospital for CT and other imaging examinations. Cerebrovascular disease can be treated with drugs to reduce blood lipid concentration according to doctor's advice. Cervical spondylosis can be treated with physical therapy.