Lately i've been having pain on the outside of my left knee and sometimes it feels as if my knee is weak. ?

I'm a college track athlete (sprinter/jumper) and I played bball through h.s. but i never had any problems until now. I spend 3 days on the track and 4 days in the weight room each weak, do polymetrics on friday, and circuits on saturday. i rest on tuesday and sunday...Anyone has any idea on how to strengthen it and just basic care? Any idea of what it could be?