What causes poor circulation? in teens?

I am a 15 year old girl. My hands and feet are FREEZING all the time. Expecially at school. My hands get so cold that they turn purple. I do 1 hour of cardio after school so i dont think its poor excersise. I dont think its bad nutrision because i am a vegetarian and i eat salads and healthy stuff. i am 5'8 115 lbs and i sometimes do faint. does the fainting have anything to do with circulation? what do you think the cause is?