After running too hard downhill like 2-3 weeks ago I got problems with my knee, it aches when I try to do squats or when I go downstairs/upstairs, i can't do anymore cycling since I have that pain in knee, when my leg is stretched everything is ok, the pain is localized at the side of pattela in one point where some kind of bone sticks out, when I try to move my skin together with patella up or down it hurts but not everytime, it's weird. What could it be?