Definitely agree with seeing a doctor.
Also, school just plain gets tougher. But this is also an opportunity to develop good study habits.
Back in the Stone Age, when I was in school, I effortlessly got great grades (as in straight A's, etc.) for years. And then high school chemistry and trigonometry in particular did me in.
But they also did me an enormous favor. I hadn't really had to study before, and then, it was imperative. So I learned how to take good notes, get organized, and how to manage my test-taking time well.
I don't use chemistry or trigonometry at work or in life at all. But I do
use the study habits I developed when trying to pass them.