Hi Brook, first of all sorry for the delay in responding, we had some issues with this site. I recommend you start with a basic blood test that checks your vitamin D, iron and thyroid function. All these 3 can be linked to mood disorders and are easy to treat through supplements.
Recognize what anxiety is: it is an over-reaction to something. Usually it involves over-estimating a problem and under-estimating your own capability. Anxiety can also be linked to feeling helpless, or feeling a lack of control over a situation. So it’s important for you to re-evaluate how you view situations. Are you, in your head, under-estimating your own ability, and over-estimating how bad a situation can be?
I recommend you get the “Anxiety and Phobia Workbook” by Bourne. It’s full of useful information and exercises that can help you. And if the anxiety is spiraling the point of impairing your life, then make an appointment with a psychologist to discuss talk-therapy options. Maybe your school has a counseling office which can be a place to start?