first go to a doctor and have an MRI, it could be somthing minor like a small meniscus tear (which is usually ok and will only trouble you in your 50s) or something worse like a cartilage defect which needs immediate surgery, unless you want to get OA in your 20s!
But for relief try the following:
Marijuana
Swimming
Glucosamine (
http://www.en.wikipedia.org/wiki/Glucosamine)
Provelen (
Microfracture: Provailen )