Thanks for posting your query.
There are many causes for pain in a single knee joint. Most common cause is Osseo-arthritis of knee joint. But it is advisable to rule out other causes also by taking an MRI
scan of the affected knee joint. I would suggest you to get yourself clinically examined by your doctor and follow his advice.
For osteoarthritis, weight reduction is the main treatment along with medicines to decrease pain like NSAID's - paracetamol
etc., Life style modifications like avoiding sitting cross legged, squatting will decrease the rate of progression of osteoarthritis. Exercises like quadriceps strengthening, swimming; straight leg rising will help in improving the muscle strength around the knee and will help in decreasing pain.
My advice would be take glucosamine
for your knee osteoarthritis
, the recommended dose of glucosamine sulphate is 1500mg and chondroitin sulphate is 800-1200mg daily in divides doses. Glucosamine by nutralite is a good brand and with balanced composition. This is usually given for 3 months and then 6 months off after there is symptomatic improvement. This is not a pain killer so additional medicines are required for pain control and optimum joint activity.
In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
Wishing you good health.