So, just before Christmas last year I tweaked my knee somehow. I don't remember a specific traumatic event, but it became very sore and inflexible, to the point where I was unable to sit cross-legged on the floor.
Putting my left ankle on my knee whilst sat on a chair would elicit some pretty severe pain in the back and lateral side of my knee, but it wasn't a 'point' pain, just generally my whole knee hurt. Also, pulling on heels and rocking over anything, or worst of all, rocking onto a heel caused SERIOUS discomfort and I had to just avoid anything that involved anything of the sort.
It wasn't really improving, but in the last couple of weeks it's got MUCH better since I've started doing some concerted stretching for my piriformis/general external hip rotation. The physio's and my current best theory as to what's wrong is an initial tweak of the lateral tendons for my hamstring and calf that's since been unable to heal due to too much torque being applied from my laughably inflexible hip. Really pleased to finally be seeing some progress, though
I know I'm just adding another ill-informed voice to the sea of vague internet advice about knee injuries, but perhaps improving your hip flexibility is worth a go if you've got niggles that aren't going away!