maybe your teacher is a prick?
i know for chemistry we get shitty exams, and that puts me off..
for the first chem exam, I studied my ass off and barely got 50%, and came 12th in the class. The reason was the test, he made up the exam and honestly it was a really shit assessment, as are all his assessments. He tries to be overly complicated with the way he asks the questions, often making gramatical errors in his phrasing too. The test had heaps of long sentences which hurt the eyes and had so little space to write your response so it messed up people like me with large handwriting.
and i'm sure that teacher has something against me.... cause honestly, whenever I put in that much effort, I come in the top 3 at least. To show the BS behind his exams, I was ranked top 3 in all subjects except for chem. After that experience, I decided NOT to study for chem at all. I ended up with the same rank as when I did study. (12th)
with you is it happening in all subjects or just one in particular? Maybe your teacher is crap? Maybe the exams are bad? There are many factors.
but anyways, i wish you good luck