Possibilities that may need to be considered include chondromalacia, tendonitis, bursitis, fractures, patellar dislocation, injuries to the internal knee ligaments/ menisci, infections/ inflammations, arthritis, cyst formation, bone growths/ tumours, nerve injuries
referred pain from the
hip etc;. I would suggest consulting an orthopedician for an evaluation and appropriate management.
Hope this helps.
Take care!