[Tiva]

Have you gone through puberty yet? Some people start really late and can't really gain weight until they start. You also may have a really high metabolism, which will slow down as you get older allowing you to gain weight. Look at your parents, if they are really skinny you have inherited the genetic goldmine that so many people want, and will probably stay skinny for the rest of your life. If they are larger and as children weren't that skinny you may actually be sick, several things can lead to an over act metabolism but if you think it is that you should express your concerns to a doctor.
In any form other than sickness one of the best ways to gain weight with a high metabolism is to work out to gain muscle mass. If people are trying to use you to look better because you are skinny leave them, make friends with people but realize that a lot of it is the melting pot of high school.
A lot of my Dad's family is extremely skinny, my grandmother is 100 lbs and eats cake every day, my cousin is a model and a size 00, and my Aunt had to put on weight to be allowed to join the air force. They complain about stores not having their size because they are so small but they all enjoy that they can eat what they want when they want it. So live in the perks, you won't gain the freshman 15 in college, you can wear your clothes from 4 years ago, you can go to france eat all of the rich foods and wines and not gain weight.
My metabolism yo-yos between overactive and slow, when I entered high school I was a size 6, when I graduated I was a size 2 and 115 lbs. I ate 4 meals a day and ran 4 miles every weekend and couldn't gain weight. I was uncomfortable with the fact that you could see my ribs, and that I couldn't control the weight loss. I wore baggy shirts and wore jeans that I had to keep up with a belt so they didn't fall off my waist. But I will warn you not to do that, it creates an unhealthy body image, it also keeps you unable to see weight gain. Wear clothes you like that show off the fact that you are skinny, to create the illusion of weight wear baby doll tops, or layer shirts. Just don't hide in your clothes, and yes there is a difference. It is having a positive body image instead of a negative one.