I have pain in both my knees and there is no swelling.i can't walk bcause of the same and i too have diabties, bp & thyroid.what medicine should i take?

No quick answer: I wouldn't take a medicine for the pain. First, you must have an appropriate and accurate diagnosis for the source of your pain. Then you can have a multifaceted treatment protocol designed for you to address the pain. Find a good local orthopaedic surgeon.

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.