Man, if you have to work this hard to get through high school, maybe college isn't for you, buddy. High school was a breeze for me; I earned a 4.09 GPA, got 5 on AP Physics, 5 on AP Stats, 4 on Calc BC, 31 ACT, and a 2100 SAT. Those are pretty good considering that I studied maybe ten times for any of my classes and never for any AP test or standardized test. In high school, the material is basically spoon-fed to you. All you have to do is listen.
When I got to college, it was a huge wake-up call. I found myself studying more hours for each one of my four chemistry tests this past semester than I did for all four years of high school. Plus I always had upcoming exams in other classes, plus papers to write, plus I was living on my own for the first time, etc. I came out of this year with a 3.6, which is okay, but not great.
There are two possible pieces of advice I can give you. 1) If you actually have to work as hard as you say you do to get good grades on tests, then maybe you should rethink the direction your life is taking you. High school should be easy for someone who will do well in college. 2) There's a chance you're actually very smart and just stress too much. In that case, don't study so much. You'll do just as well (if you use time wisely in class, that is), and you'll enjoy life a lot more.