Hi.
If your vomiting is out of your control---in other words, if you're not purposely making yourself vomit...and I get the sense that this is the case---I would first recommend that you get a physical to make sure you're okay and that your anxiety is not masking some other illness.
Dr. Sharon Bud, a specialist in adolescent psychology, says that the pressures on teenagers, particularly girls, are increasingly more severe. It's no wonder some teens are "somatizing" their stress---turning it to physical symptoms. There are several things she recommends to manage stress. Exercise works wonders--the body produces chemicals that help elevate mood and create a sense of calm when we exercise. You might also want to look into meditation or affirming visualizations. One technique Dr. Bud suggests is allowing yourself a time-limit to worry. Say, "Okay, I'm really feeling anxious. I'm going to sit with this for fifteen minutes and then I'm going to get on with my homework." During this time, take the anxiety from a generalized, and, therefore, unmanageable place, and make it more specific. What in particular are you worried about? State the problem and see if you can find another way to solve it.
If this extreme anxiety persists despite these attempts, it may be time to see a mental health practitioner who can provide a thorough evaluation. Ask your parents or a trusted adult---your school counselor, for example---for help in finding a referral.
I hope you feel better soon!