Well, without an evaluation it would be difficult to determine the cause of the knee pain. Possibilities that may need to be considered include patellar dislocation, chondromalacia patellae, infections/ inflammations, arthritis, bursitis, tendonitis, cyst formation, iliotibial band syndrome, osgood schlatter disease, bone growths/ tumours, nerve impingement/ compression, fractures, injuries to the internal knee ligaments/ menisci etc; just to name a few. I would suggest consulting an orthopedician for an evaluation. After a cause is diagnosed, it can be managed accordingly. Meanwhile I would suggest resting the knee and avoiding weight bearing. Tylenol/ OTC NSAIDS may be helpful for pain relief.
Hope this helps.
I am experiencing the exact same thing! I was also looking through threads amazed that no one mentioned swelling, until I came upon yours! Please tell me you found out what it was!