Anything just below the knee cap and towards the outside screams IT Band to me. Might be worth getting to a sports therapist or physio and get it checked out. I had ITB probelms for years and all the pain was where you are describing it. My friendly sports therapist with evil elbows of steel sorted them out eventually.
Sounds like it could be your IT Band. Definitely get yourself to a physio or sports therapist for a session and some advice on how to stretch it. If it is the ITB its a tough one to sort out. Mine troubled me for years. Only now have managed to get it sorted with some sports therapy and using a foam roller regularly.