I am 60 yrs old lady with a thin body type but still I have the problem of knee and leg pain. What should I do?

Many possibilities. Your pain could be as a result of many different things. A thorough history and physical exam and possibly some laboratory and radiology exams are needed to determine the exact cause. Causes of pain may include: trauma (fracture, tendon or ligamentous tear, arthritis), infection, metabolic conditions (gout), musculoskeletal or biomechanical abnormalities.