I was in my 40s before I learned that my "mental" condition is caused by central nervous system dysautonomia. I used to think it was all my fault and if I would just do better I would do better. I thought it was just a matter of discipline.
Finally, when I was 40-something, I got an accurate diagnosis, but it was another 20 years before I found out about SSRIs, which help somewhat. I wish I'd known ages ago that I have a real disability. But back when I was a kid it wasn't OK to be not OK.
I think I'd have been a lot happier if I hadn't been trying so hard all the time to fit in and just be OK and never fully succeeding. I've told a few people I thought I should deserve an Oscar for acting -- I was half joking, but I was seriously trying to be what I wasn't almost all the time.
And I think it was exacerbated by at least one head injury after I was grown.