I can’t provide a diagnosis on the basis of a letter, of course. But I can tell you that if you were seeing me for an evaluation, I’d be checking for anxiety. It’s possible that in high-stakes situations, your anxiety gets the better of you. If that’s the case, the good news is that some coaching in coping skills is probably what will be most effective.
I encourage you to seek out a mental health professional who can hear your whole story and who can give you recommendations for management of your symptoms. There is no reason to wait and possibly waste another year. You are smart and articulate. I think you will make good use of therapy.
I wish you well.