Walking up the stairs i felt a slight pain in my kneecap. i can walk but i feel my kneecap. i cant fully bend it. i dont see swelling. what to do?

Get evaluated: Patello-femoral knee pain (pain behind the knee cap) can have multiple causes including but not limited to trauma, infection, and neoplasm. Patello-femoral pain can be very common and some rest, NSAIDS, and therapy are usually helpful. A thorough history and physical followed by diagnostic imaging can help get the answers and treatment you might need.