Knee pain. To relieve this pain.

Sir, I am Prakash.I have knee pain for last 3 months .At the early stage ,it occurred intermittently only while riding bike.I travel daily 20 kms in bike to office.Then I started using bike rarely to office and for some days my pain was relieved .Again when I started using bike, it got worse .Nowadays if I sit in my chair in office continuously for min1 hour I have pain or when I fold my leg it's paining .If my pant touches my knees as well I feel painful(like I had cut my knee with knife). I consulted a physiotherapist and they taught me knee pain exercise which I did daily.it will relieve my pain at that instant again my pain starts.please suggest some treatment to relieve this pain. Thanks Prakash.