How can i deal with my stress?

I feel so stressed out and worried right now that it is making me feel sick. Im only sixteen, i know that is way to young to feel this stressed and yet i feel like im going to die from it. My school work load has been extreamly stressful, i feel like I never have any down time and I am always worrying that im not going to have enough time to get ignments done, or they arent going to be very good and im going to get a bad grade on something and its going to affect my future and carrer and plans for collage. My brother is out there at collage and has known exactly what he wants to do with his like since he was like 10 and i still have no idea and cant make up my mind which just adds the worry that I will never do anything and end up broke and desperatly looking for a job. plus i need to get a job sometime soon and i need to finish drivers ed and im falling behind in some of my school work and im afraid im going to fail math because i just dont understand half of what the teachers talking about. then there are my responsibilities at home that im not doing lately. i feel like its all too much and I dont know what to do. and to top it all off i have gotten to a point where i feel so stress and worried that it is interfiring with my school work and i feel like i know i cant do it all so why bother or im so worried that everytime i try to do something i think of something else but i dont want to do any of it and gaaahhh i just feel like my heads going to expload sorry for the long post and all the typos but please someone just tell me how to make it all better.