It sounds like you're getting a great amount of exercise in! Now, all you really need to pay a lot of attention to is how much you're exerting yourself. For example, if at your 90 minute P.E. class, you're mostly sitting around or talking to friends, it's probably not giving you as much benefit as it could. I suggest start jogging after school:) Start with 1 minute jog and 4 minute walk(repeat the pattern), then, as you get more comfortable, increase the running minute and decrease the walking minutes. That's what helped me build up my stamina! I run a lot now, and still have occasional lazy moments. It will go away once your body learns how much endorphin it gets from exercise:) Hope I helped!