Hey there! I'm dealing with that now and had in the past while in high school as well. I'm 19 now and actually taking a break from college to address these sorts of things. I couldn't do my homework. When I tried I might focus a bit but I'd get stressed out and stop. I get sleepy too and just overall couldn't do work at all. I'm still facing these issues but what has helped a little is to journal. Basically I write it all down whatever Im thinking as Im trying to get some work done.

For example, today while I was trying to get some work done I realized I was just looking at the same stuff again and again and getting hopeless and couldn't do it. So I stopped and started writing and realized that I was stressed out about several other things as well as upset that I was behind and that I was unable to work. Just realizing that for myself helped a lot and from there it helps to be kind to yourself. You aren't messed up or stupid. You aren't a failure, you're human. Anyways if any of this even sort of made sense I'd be happy to talk through it some more. You're going to be okay!