For me ice doesn't do the trick I had to wear brace for sometime because it used to hurt so much that couldn't walk on it and to make it worse my high school is like a campus which consists of have a 20 pound back pack walking up and down 2 or 3 flights of stairs and walking a mile each day.
It sounds like you are young (in high school)... since you haven't a serious knee injury I'm pretty sure you knee pain is directly due to over-developed and over-tight quad muscles. If you quad is too strong and tight, it will literally pull your kneecap out of it's groove (which not surprisingly will cause kneepain). You need to roll them out (and you IT band) on a foam roller
and stretch them
My info might be out of date... but last I checked your quad to hamstring strength ratio should be something like 2:1... and I bet your is way imbalanced (probably like 4:1 or even 6:1)... and you need to strengthen you hamstring a lot to balance out your huge quad. I would do a lot of bodyweight single-legged deadlifts
(don't bother with weights as that requires hands on instruction to avoid wrecking your body... with this variant... you will know when your form is bad because you will fall over!)