Knee unstability, pain and knee lock.

I am suffering from constant knee pain since last 5 years. There is a click sound in knees when I bent them and the knee cap is not very stable...the knee also gets locked at times..the problem is getting worse..I used to be an active person with jogging and running.. now I cannot walk without pain.. Can't take stairs or sit down without support. I consulted a many places... Took calcium and vitamin d supppiment...went for physiotherapy...number of x ray but nothing worked.. Calcium caused me gas and pain killers just subside the pain.. inspite of being vegaterian I tried paya soup for 2 months.. Nothing seem to help... Am I suffering from arthritis? Do I need knee replacement.. I would like to get back to active and control the weight and lead a pain free life.i am looking for serious help..suggest me if I need to take specific tests..or where can I visit for free consultation