Hi welcome to Health care magic forum.
Thanks for choosing H.C.M.Forum.
After running about 2 km got sudden pain, on lateral side of knee, continued another 500 m,then to walk about 2.5 km to home, at first there is pain to bend, then to extend.
It appears to be the stretch of the lateral ligament of the knee. It needs to be treated with
elastic bandage, rest and analgesics.
I advise you to consult an orthopedic surgeon for diagnosis and treatment.
I also advise you to avoid potato, other tubers, tomato, egg, chicken, and seafoods, to avoid the pain, till it is completely comfertable.
Wishing for a quick and complete recovery.
Best regards.