Im 15 and play tennis for my school team... ive been noticing similar pain as what your describing like in the knee and on the sides. mine hurts on the right, left and bottom and center sides of the knee where you said yours hurt. mine doesn't hurt all the time, only if its in a position for a while, i stand up, go up or down stairs sometimes and when it gets stretched out.
i first started noticing it like half a year ago
when we would do excersices like lunges. it hurt but slightly. i thought i could try to do them better but i was allready doing them correctly with my knee at a 90 degree angle and back straight. my coach said that if our knees hurt to tell her, but it didn't hurt much so i decided not to. since then it had been getting worse when i would excersice. then i hit that knee falling on the bleachers, it ran into the corner of a wall while running. its not been bruised or swollen or anything. but now my knee hurts like i described above.
anyone know like excactly what it is, and not just guessing. i'd really appreciate it so i can tell my coach and she can figure something out before it gets any worse.