I am severely ADHD. Support groups and forums are a load of crap.
The first thing you need to do is realize everyone has problems and yours is that you have trouble concentrating. People have been doing much more, with much less, for much longer, than us and with the same problems. Monks memorize libraries. Scholars learned seven, eight, and twelve languages. And some of them had concentration issues.
Suck it up and don’t be a whiner about it.
Second, make lists. Lots of lists. Write everything down immediately, keeping the lists with you, and update them constantly. Look at the list and assess how much time you have left to do things, and take pride in eliminating things off the list.
Third, find a place with good distractions. That is, a place where the distractions are brief, like a coffee house where you can chit chat briefly then get back to your work. It’s easier than home, where you will go off on hour-long tangents.
Fourth, reread #1. It’s not an excuse. It’s not even an explanation. It’s who you are, and no one cares, so learn to work with it.
Sincerely, with love, from one ADHD kid to another.