Welcome to the forum, mission,
Nobody likes to suffer from anything that makes them feel uncomfortable or out of the norm. First off +1 for going and seeking a doctor's diagnosis. I've spent a lot of time online researching and trying to find the answers for my own diagnosis and nothing spelt it out better than visiting a doctor. With the information I got from that I feel that I know myself better and I know what I'm up against.
ADHD, though I know what it is but not too knowledged in it, can be a pretty overwhelming. Do you always feel the urge to move about? I'm always curious to hear more about these kinds of things.
As for the late diagnosis, It is a bummer than it has affected your high school experience but just understand now that knowing you are faced with this situation you can continue to live a happier lifestyle without that always constant thought in the back of your head as to "What's really going on with me?"
Are you planning on continuing further schooling into college? I'm not only going to college because I want to score a degree, but I mainly do it to keep me occupied, and motivated.
Keep in touch man,