I struggle with anxiety at different times during the year and I work in an office/court setting. When it gets really bad, I sometimes wait until I can be alone and then vent. I feel like it is trapped energy that needs to be let out. Regular exercise certainly helps and vigorous exercise when there is a harsh buildup is a great solution. Perhaps any breaks you have at school can be used to do breathing exercises or maybe go to your car and turn the music up loud and just growl! Whatever works for you -- just remember that when you do find something, you need to stay vigilant to catch the proper times for you to use a technique.
"Even when the sky is heavily overcast, the sun hasn't disappeared. It's still there on the other side of the clouds." - E.T.