My advice is to consult a psychiatrist to find out if your problems are memory related, and not just psychological stress. Because from my experience as a student, the A students had a common trait, which was they never got scared over exams. Some of them used to take it so lightly, they used to sit, and laugh and about it - even after 'thinking' that they did bad. surprisingly,they ended up with As most of the time.
Hope I helped,
Regards,
IGNORE INC.