My 'guess' is knee tendinitis. Has happened to me before and going up and down stairs was extremely painful. Orthopedist will probably give you an anti-inflamatory and say take two weeks off. Didn't work for me, so I went to an Active Release Therapy guy. Two sessions and some new stretches and I was back to normal.
ITB or tendonitis, I've had both, I found ART to be more effective (and faster) than orthopedist.
ITB or tendonitis, I've had both, I found ART to be more effective (and faster) than orthopedist.