Okay, so I'm a bit older than most of the other posters seem to be, but here's my take on it. I'm currently 28, was easily the most 'gifted' student in my (small) school, and spent my entire school career feeling unmotivated and not doing very much, or doing very well.
Over ten years later, looking back, I'd say that my problems with motivation weren't quite what I thought. In retrospect, there were plenty of things that I genuinely cared about. At the time, I really didn't think so....but ultimately, there's no way my life could have sucked so much if I hadn't cared about things. If I didn't care, I couldn't have been hurt; I did care, and I did hurt.
Now, at least for me, high school was the hardest time of my life. As a student (and a minor), you have almost no control over your life. There are incredibly strict limits on how you live, what you do, and who you feel that you can be. I wasn't motivated because none of the options I saw open to me were very appealing; they all required hard work, in return for things that I simply didn't care about. If you're feeling like this, it's natural to feel unmotivated; nobody's motivated to work hard at unpleasant tasks in exchange for unpleasant or meaningless awards.
Now the good news: life gets much, much better after high school. You have more options than you think you have. When you get control over your own life, you can work towards things that actually matter to you, and build a life that you actually want to live. You will still have to work hard (there's no substitute for that), but it's possible to find work that you actually enjoy, and to actually enjoy the life you get by working.
Probably the best advice I can give you is to spend some time working out what's really important to you. Find the things that inspire you, the things that you care about. Ever read a book, or watch a movie, or read a news article, and think "I want to do that/be like that/do something about that"? Pay attention to those things, because those are the things that can motivate you.
Bear in mind, too, that these things don't necessarily have to relate to academics. Maybe you want to live in a house on your own, or move to a big city, or live in foreign countries, or date someone interesting. Maybe you want to go to a specific college, or take a year off before you go to college, or not go to college at all. These are all valid and important choices, too, and they're things you can begin working towards now.
Anyway, as long as you're still in high school, there's going to be a lot of stupidity that you're going to have to put up with. There will be classes that can make interesting subjects boring, there will be pointless and repetitive homework assignments, and there's going to be a lot of really surreal social drama. As an adult you'll have a different set of stupidity to deal with, although you'll have a bit more control over which crap you deal with. But as you figure out what you really want to get out of life, you can find a lot of valuable things in the most unlikely places -- even including high school. And ultimately, once you've got some goals that matter to you, personally, and once you've got a life you can truly enjoy, you'll find that all the stupidity gets a lot easier to deal with.