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!
Hi there!
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.
Take care!