What causes skaken in the hands, dizziness, nausea, and passing out?

I have had this problem since my sophomore year in high school i am currently 18. i start having slight shakes but i do any activities like laundry, cleaning or even walking my shakes progress and i become nauseated and dizzy, then i pass out. back in high school i would have the shakes for may 30 min to an hour then they would go away and i wouldn't have them for a while. now for the past couple of days i have had the shakes constantly. its more like jitters and i can lay down and sit for awhile and it still want go away. i use to sit or lay down to calm it back in high school and now that doesn't even work. i have been checked for low iron and sugar back in high school and the doctors said nothing was wrong and i was just shaking. i'm 5ft 4 and weigh 110 i eat and drink like im suppose to so what could this be?