My stress is affecting my health how can i change this?

i'm 18. i react to everything with stress it seems like, and i hate it. i'm always stressed (just like my dad, 2 aunts and grandpa) i constantly feel like i'm supposed to work and I feel guilty if i relax. i feel like all homework that is actually due next week was supposed to be done yesterday. i lost one of my text books and am behind on a car payment and am freaking out. i am very impatient and like tasks to be completed promptly. im never doing too many things it once they all need to be done NOW. i feel like i'm a failure at most things. my grades suck i couldn't even keep a 3.0gpa this quarter. my health is deteriorating. i've been gaining weight, dont get enough exercise, and developed depression and bulimia nervosa. (i take prozac but refused therapy because i felt like it was a god awful waste of time and money) i feel sad and tired most days and desperately need to change this.