Well, without an evaluation it would be difficult to identify the cause of knee pain in your case. Possibilities that may need to be considered include chondromalacia patellae, tendonitis, bursitis, fractures, patellar dislocation, injuries to the internal knee ligaments/ menisci, infections/ inflammations, arthritis, cyst formation, bone growths/ tumours, nerve injuries etc; just to name a few. I would suggest consulting an orthopedician for an evaluation and appropriate management. Meanwhile you may try resting the knee with some OTC NSAIDS to relieve the pain.
Hope this helps.