How can I motivate myself to study and learn without getting frustrated?

For some background, I'm 18M, I dropped out of high school 2 years ago. Since then, I've had almost no responsibilities. I've had a really long struggle with mental health and every time I'd start being productive, I eventually gave up because of my depression and lack of self-discipline. There's been times where just getting a quick shower feels like a monumental task, so how am I supposed to sit and learn for hours at a time? I've been trying to learn coding languages and stuff since that's something I've always been interested in, and when I'm motivated and feel like doing it, I'm really good at it, but 90% of the time it feels difficult to push through (as with learning literally anything, even if I like it).

Any time I try to learn something if I'm not in the mood to learn, I get this really hard tightness in my chest and tingling in my body, then I eventually get really frustrated even when it's something I enjoy learning. The act of forcing myself there makes me physically uncomfortable, but I don't know how to get rid of it... I kinda have to though, I'm working on applying for GED prep classes soon while holding down a job at the same time and I know that I'm going to get frustrated having to use most of my freetime to study. After that, I wanna go to college, but that's not gonna happen if I can't get this under control. I appreciate any and all advice.

(And no, I will not join the military. People that do are awesome, but it's not for me.)