Man, why are you doing so much? It's not necessary to do all those things in order to satisfy the brothers that you're a believing Witness. You need to consider your mental health. As Justnowout says, you should ask the appropriate brother(s) if you can temporarily put some of your responsibilities on hold. Pick the things that are most stressful to you and put those on pause. You may never want to resume them again, but you and they don't have to know that right now. Just ask for a temporary reprieve. Are the most stressful tasks the talks and the reading for the study? Then talk to the school overseer and the Watchtower conductor.
If you have the appropriately contrite expression on your face when you speak to the brother who is in charge of whatever area you need to do less in, then unless he's a jerk and doesn't like you, he won't give you a hard time. Even if he does give you a hard time, just squirm and look pained and refuse to give in to his pressure. You can honestly tell him that it's causing you too much stress right now. Guess what? He can't make you do anything. Some brothers will even just take someone off their list lickety-split if they're asked nicely, without making a big deal out of it.
Frankly, you sound like you have a problem saying "no". Usually this stems from being overly concerned with what others think. It gets easier to say "no" when you get older, but there's no time to start learning like the present. Don't worry about what he'll think of you -- "Will he think I'm spiritually weak? Will he just plain think I'm a wuss? Will he suspect me of not being a genuine JW since I 'should' be able to do these things and go to college at the same time?" -- just shut those thoughts out of your mind. They don't matter. The brother in question is just a nudnik who believes in silly things and, while he may matter to your world as long as you're an active Witness, some time in the next few years he won't matter at all.