I feel so stupid it's not even funny.

I'm not one to usually share my experiences with random strangers on the internet, but this was the only way to get things off my chest. I'm taking Calculus AB at my school and I'm borderline failing. It feels like I'm understanding the concepts yet no matter what I do, I can't seem to display them well on any quiz or test. Like at home I can do practice problems completely fine at home but then on the test I fuck up literally everything. I don't think I've ever gotten a 70% on any quiz or test in that class and its extremely humbling, frustrating, and even embarrassing. Today I had a quiz and it was 2 problems, 20 minutes. I blanked out so badly I literally didn't know what to do for the first problem and half-assed the second question. I go to my next period and resolve the problems, and everything is peachy. What the fuck. 1-2 weeks ago we had our chapter 3 FRQ, which I fucked up badly on that one as well...and yet I knew what to do for every single fucking problem. I feel so dumb in comparison to anyone in my class because they're doing great on their quizzes and tests, yet for some reason I just fucking can't. No matter how much extra tutoring I do, no matter how many extra hours I put in watching my teacher's videos, nothing seems to be working. It's hard to even fathom how much I've fallen considering I usually get an A when it comes to math. I don't think I've ever hated myself this hard as I do now.