Why do I suddenly suck at school?

For the past two years of high school, I got really good marks in all of my classes, like mostly 90s. When this school year started, I don't know what happened but I'm so confused in all my classes, I feel like I'm not understanding things as well. Now all my marks are around 70 to low 80s.

The whole thing just makes me even more unmotivated, and even though I try my best on homework/assignments and studying for tests, it doesn't seem to get any better. Maybe I'm already burnt out? But it makes me stressed too, since I definitely need better marks to go to university.

T-T

Why do I suddenly suck at school?
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