really bad anxiety-does anyone have any advice?

i have severe anxiety, i get anxiety attacks in classes, while studying, and while taking tests and quizzes. i have 9 classes and im in the 8th grade, plus im taking an AP exam, and im ADD(inattentive). i know that makes it very stressful, but ive has the worst anxiety that ive ever had. during tests and quizzes, i start shaking and i blank out, as well as feeling light headed. in class, the only thing that differs is that instead of blanking out, i cant focus on anything. both of these things have caused my grades to drop rapidly, which has an effect on me even more so than it may for others, because im a really hard worker and it feel like it is all for nothing. one of my teachers pulled me aside and talked to me about my anxiety before a quiz and one of my other teachers talked to me about it in a student support. two of my teachers other than the first two also know about my anxiety, but they havent said anything to me about it(i only know because my schools special ed coordinator told me). but my grades are dropping because of this anxiety, and i dont know what to do. im normally an a/b student and ive started getting cs which i know is very unlike me. how can i stop the anxiety attacks during tests? i take tests in a separate room and i get extra time. should i talk to any of my other teachers about how i think my anxiety may be affecting my grades, and should i talk to the teachers who i know know about my anxiety? or is that a bad idea? also how do i prevent my in class anxiety attacks? i know those four teachers notice my anxiety attacks, one of my teachers tries to help me out with a problem when i get the anxiety attacks. i dont leave the room when i get these attacks, but my anxiety attacks are daily. does anyone have any ideas for me to try? my anxiety is making everyday a continuous struggle, it really takes a toll on me, i feel really sad all the time, ive never cried in school, but ive been pretty close to doing so in class. i would really appreciate the help!!