You may be an introvert, you may be quiet, but you're not stupid. Maybe you feel as though you are because you can't relate to others as well, or it may affect you in school, but its usually those who don't know they're "stupid" that are. You're young and should be able to change the direction of your troubles. Therapy/counseling might help, although I know for me its a non-starter because I don't like to talk about my problems to strangers, and anyway there is nothing they can tell me or suggest, that I don't already know. Take it day by day and try not to think of it as a long term thing. Once you give in to it, it only gets worse, so don't. Everyone lives life differently, and you shouldn't base yours on just those around you because of it. Get youself a hobby. Maybe indoor growing of plants/flowers that give a challenge, or just anything you like to focus some time and attention on. Good luck to you!