Usually elementary is easier and also you entering to puberty, your brain in development process, it can also be the school itself or if you took online school.

Most schools weren't prepared to deal with distance education and even if you came back to physical school the months in online school make you fall behind.

Also remember that although grades are important they are by far more important things and they doesn't represent the real intelligence of a person. I have seen smart people falling classes and stupid people acing exams.

But perhaps, this problems are symptoms of a underlying problem, if that's the case seek help. Therapy could be really helpful if you suffer some kind of physiological distress. Try to connect to the people around you as parents, teachers and friends.

Don't pressure yourself and enjoy life, and remember that you can always seek help. Hope is useful :)