Why Do I feel weak and exhausted when i think about studying and school? 14 y/o?

High school is tough. I remember when I was 14 I used to dread going to school everyday. But looking back on it, apart from detention's, you can't get in any trouble for not doing the work so just take it easy, chill out and let yourself slowly ease into the cirriculum. Don't force all this school work down your throat when you're clearly not ready for it. Just do something small: really small. Maybe spend 5 minutes in class writing notes and then reward yourself by spending the next 65 minutes (or however long each period goes for) mucking around and having fun.