What classes should I be taking in highschool/college? I want to be an ER nurse?

I am seventeen, and a junior in highschool, I make fairly good grades and am certain I want to work in healthcare. I want to become an rn and specialize in emergency care for a few years and eventually go to medical school to become a doctor. My family cannot help put me through medical school so I will have to be a nurse for a long time to earn the money to do it by myself. If anyone can give me any advice at all it would be greatly appreciated.