I know exactly how you feel, I used to go through this in high school as well. Actually, I think all of us have to go through these periods in our lives. I'll tell you a true story.
I remember growing up in NYC a few years ago (I'm only 26, so that's not TOO long ago), and being very miserable at home. Actually, I had nothing to complain about, we had everything we wanted, but I was very unhappy and miserable, specifically, I disagreed with my mother a lot on just about everything. There were times I just wanted to run away, and school wasn't going that great either. Sometimes I came so close to just ending it. After one particularly fierce fight, I decided that I just didn't want to live anymore. I was so amazingly depressed and felt so worthless. I felt as if my mother just sucked all the life out of me every chance she got. I locked myself in the bathroom, and just refused to come out. I was looking around in vain for something to do, something to take, something to just end it all. I reached into the medicine cabinet, and started unscrewing the bottles. Next thing I knew, I was emptying the contents into my hands. My hand was now full of multi-colored pills, and I was nervously contemplating the unthinkable. What did I have to lose? No one understood me, I had no true friends, I felt as if my life was going nowhere at 15. Heck, I'm gonna swallow. Just at that moment, the doorbell rang. It was one of my mother's friends from our church who was especially fond of me. She was driving around in the area, and just decided to stop by to see if I wanted to go out with her for the evening. I really wasn't in the mood, but she just looked so excited with a sense of urgency that I unwillingly said yes. Well, that night turned out to be one of the best in my life. She took me out to a concert, and we had such a great time. When I came home late that night, I was all full of life and happiness. I didn't mention to her what had happened, but somehow she just managed to change my mood. As I was taking my pants off to go to bed, I heard the pills spill from the pockets, scattering all over the floor. I was shocked! I had completely forgotten about them, and was so angry with myself for ever even contemplating such a stupid thing. I vowed to myself since then to love myself unconditionally, and to never ever think of such a thing again.
I've never forgotten that promise, and I am so happy I never swallowed those pills. Since then, my life has just gotten happier and happier, and I can't imagine throwing away all this happiness because of teenage crisis.
Trust me dude, things will get better. The best you can do now is just love yourself. I know, it sounds stupid, but this is the greatest thing you can do for yourself. By loving yourself, you build your self-esteem, self-confidence, you develop discipline to accomplish the things you want to do. It's all within you, you just have to bring it out. Don't worry yourself about those kids from school. The biggest secret is, there're feeling just as insecure and nervous as you are, that's why they form cliques and in-groups. Sometimes they will even try to put you down so that they can feel better.
Do your own thing. Do what makes you feel good, as long as it doesn't harm anyone else. Pursue your hobbies, remain in school and study hard. In the meantime, start planning. I can't stress this enough, most teenagers are bored and feel worthless because they have no plans. Well, now is the time to start. What's your purpose in life? Look at what you're good at doing, and what comes natural to you to find the answer. Make your goals and start working towards them. This will take your mind off the rejection you get at school.
As for girls, be yourself. Time and time again, girls will tell you they are most attracted to guys that are original, self-confident and most importantly, those that have a plan, a goal in life. Don't approach a girl if you're horny, bad idea! I know how those hormones can rage! Instead, talk to a girl like you'd talk to your friends. Be honest, don't try to be something you're not. Women appreciate that. When you get to the bottom of the story, you'll see that those girls interested in jocks and the in-group do so because of the attention, and again, insecurity. Most likely, you will not be happy with such women.
Also, don't forget that our teenage years can be quite awkward. Your body is changing, your hormones constantly make your horny, you're beginning to form your own ideas and so might be confused a lot. Do research. Read. Look to people more intelligent and experienced than you are for advice. Never be afraid to ask questions. Stay away from those that ridicule you. Stay especially away from negative people, they will only try to make you weaker.
If you continue to love yourself, build your self-confidence, plan and work towards your goals, in a few years, you will become a force to behold.