How do you press on?

I'm not talking about suicide, or life in general, mostly because that it's whole own can of worms. But how do people with depression and/or a depressive disorder continue to do well in school despite carrying such a heavy load?

I'm a sophomore in high school right now, so I'm especially scared for next year when I'm planning on taking three APs and getting a job. And since I'm struggling with depression (I haven't been diagnosed but I find it very unlikely I don't have it), I find it INCREDIBLY difficult to carry on with my studies. And even if I don't have it, I just went through a major breakup with a friend, so it's more than a little difficult to not just fixate on that.

And to make matters worse, I used to be really good at school and never really had to try, and now I actually do since I'm in genuinely difficult classes (AP Euro right now), I don't actually know how to stay motivated. Rather, I just wait until the stress becomes so bad that I manage to finish everything on time.

And please try not to include the usual "hang out with friends", "spend time on your hobbies", "eat foods you love", or any of that, since for almost all of them, I'll have a reason as to why I either can't or am not able to. Other than that, any advice would be appreciated. Please and thank you.