I'm forced to go to school even when I'm sick
Have you talked to your parents about how you feel?
Yes and my parents still force me to go.
If you are not feeling well at school, you can let your teacher know and ask her if you can go to the school nurse. Even if your parents don't have arrangements for you to stay home, you can still rest a little at the nurse's office.
I'll move out if they don't do what I want.
I don't think it's legal for you to leave home if you are still a minor. Try having another discussion with your parents about how you feel, maybe you can learn to understand each others point of view.