Definitely agree with weight training taking stress off your knees/legs for the long term.
But it could also be growing pains. When I was in 7th-8th grade my growth spurt started and the first thing to start killing me was my knees. Then I had another growth spurt in 10th grade and my back was killing me. Nothing you can really do about it except ice yourself after every practice and wait for the pain to go away. But the good news is once you grow out of it, your knees will be fine until you're in your late 20's/early 30's (if you're training right).
And uh the most obvious thing is keep fat off your body.