What Causes Severe Pain In Knee Joint?

As I am looking down at my right knee, I have a frequent stabbing pain just to the left of midline of my kneecap. I also have Osgood-Schlatter. The pain occurs in the joint and is severe. This has been going on since the first of Sept. The pain has become more frequent recently and occurs when I am resting. It is sudden in onset. I am a 58-year-old overweight female. I just took prescription Naprosyn. Any suggestions?