I'm a 17 year old high school student.
I try to explain my problem using a short example:
During a maths test I have tried to remember a formula, which I just learned a few days before. Normally I know this formula immediately but in this test I sat there like I would have never seen anything of this stuff before. After about three minutes I finally thought I would remember this formula again, but I did not. The formula on my paper was not correct, though I thought it would be. Then there were some other mistakes like hitting the wrong buttons on the calculator and so on.
Seems like I cannot be productive under pressure.
Any advice would be great :)