Ok, great. That's great. I had the same feeling you're having, from 13 to probably 21. Same exact fucking depressed feeling all day long, wishing to die or just disappear. Things will get better, trust me. Things will turn around for good people. You just have to hang in there. All these bad stuff happening to you will shape your character. Just keep studying and life will change before your eyes. Just try to see the positive out of everything. In school try to look at the good stuff you're doing every day, if you get a good grade, if you learn something new.
If you are afraid of cancer, try to run yearly tests, be careful about what you're eating, all that. Try to live healthy. I'm 25% prone to get cancer in this life, so I'm being extra careful also.
How is red hair a problem to people? hahaha. Everyone like to hate something about themselves. Some people hate they're bald, short, tall, whatever. I used to hate that I have brown eyes, because I liked blue. And I met people that hated they have blue eyes. You'll always find something you have about yourself. But try to look it the other way. You have red hair. How is that a bad thing? It's not. Unless you don't take care of it, then yes, it might look bad. But having red hair is not BY DEFAULT a bad thing. Just embrace it, is your natural color, wear it with pride. Don't be ashamed of who you are. If you hate it or love it, everyone will agree with you no matter what. It don't matter to other people. They see what YOU see. If you start loving it, they will start loving it.
Oh, and people just look like they have "jully lives and 90% success rate". But they might be just like you, having a hard time. 99% of the cases, people are not how they look. Try to talk with some of there 90% success rate people and see how they really are. I bet at least half of them have way bigger issues than you probably. But they choose not to show it. It doesn't look good. Act it till you become it.
I emphatize with you a lot so let me know if you need any more help.