Do you have any idea why you might be having anxiety? Can you talk your parents or school counselor?
Just like me. You have to push you self and see a doc and get on meds if you need them. Good luck. :)
This sounds more like ADD than anxiety, though both can appear similar to each other.
I have really bad attention span issues, and everything you describe sounds similar to what I go through every day. I also have anxiety and depression, but they don't seem to affect my schoolwork/concentration as much as my lack of attention span does.
Me, I find that exercise, rest, abstaining from caffeine and alcohol, and avoiding distractions helps best.