What Causes Pinching Sensation On The Lateral Side Of Knee?

Hi. I am a 26 year-old female and recently I have been experiencing a lot of pain on both my knees. It doesn t hurt when I m standing, walking or being active overall, but it does hurt when I sit with my legs folded (it hurts on the sides of my knees) also when my knee is bent with my foot flat on the surface. A little while ago I was also feeling a pinching sensation on the lateral side of my knee whenever I kneeled down and put pressure on the knee. Afterwards, when I walked, I would feel as if my lower leg is loose and not attached to my upper leg.