If its any consolation I had the exact symptoms you last year. Came out of nowhere. Kneeling down, climbing stairs and going down, and bending were a painful. Hurt on the backside of my knee to the touch and when moving. Had some swelling. I’m no doctor but it could be a medial patellar retinaculum strain. I believe that’s the correct spelling of the diagnosis my orthopedist gave me. Some physical therapy and ice, ice, ice and it went away. I had to push it though and push through the fear of it hurting before it really got better. Nursing it made it worse. I thought back when I was being really lazy for a month or two, I think that’s what caused it. Hopefully that’s all your problem is but definitely get it checked out. I thought the worst but mri showed no issues except some early arthritis.
