I have been affected by anxiety since I can remember. When I was 8 years old, my friend in ballet class used to call me the "worry wart." I was always so concerned with details, concerned with doing well, afraid of messing up.
In middle school during English class, the boy behind me kept kicking the back of my chair. After a few days of this, I finally worked up the nerve to turn around and tell him to quit, only to be immediately yelled at by my teacher. She didn't see the whole situation, she just saw me turning to tell off a boy. I was so embarrassed, I cried.
In high school, I began to experience panic attacks and night terrors. My dad took me to the doctor and after being treated for ulcers I had developed from stress, I was diagnosed with a panic disorder. In large classes, I would become so overwhelmed by hearing all the talking during free time that every few weeks I was getting in trouble for walking off campus and going home without informing anyone. After my diagnosis, I was allowed to sit in the counselor's office if I needed to leave class and she would do paper work while I read Alexander Dumas.
Being young is weird. I'm not all grown up yet and I think I'm starting to realize that that simply doesn't happen for anyone. If I could tell my future-adult child-having self one thing, it would be to promise to never EVER tell your kids (teenagers) that "You'll understand when you're older." You won't. You will just get more comfortable with the fact that not every thing can be understood. Adults don't have some superpower that allows them to understand everything. A lot of adults give up trying to understand. The healthy ones learn to accept their humanity and accept their reliance on the unknown, and they are okay with that. Other adults get bitter about being so insecure. They are dicks, don't be like them.
There is truth though, to the statement "You'll understand when you're older." Basic biology teaches us that the frontal cortex of the brain has yet to fully develop and this helps you process your perception of the future (1). Right now, every thing seems permanent, there is no future and your life now is all that you can chemically understand. Add in a dash of childhood pains, hormones, growth spurts, and general awkwardness and you've got the makings of a really great emo band.
But that's the truth. You won't ever understand but as I'm sure everyone has already told you, it does in fact get better. Happiness really is what you make it and if that is true, then you not only have the opportunity but the responsibility to find what makes you happy. There isn't room for more bitter, insecure dicks in this world. You have to work for this happiness and it's hard work. You can't simply get a job and buy more makeup to be happy. You can't join a gym and look like -who's a popular hottie these days you kids all like?- to be happy. You can't make good grades and satisfy all your parent's expectations to be happy. You can't kiss ass and make everyone like you to be happy. You can't get super rich and buy a bunch of friends to be happy.