Hi OP, I'm sorry that you are struggling. I have late diagnosed ADHD and there have been times in my life when things were completely out of control- masses of debt, nearly kicked out of college for not turning up to anything, chaotic living environment, risky behaviour with sex and drugs etc.
Now however it's a different story and I think people who don't know me well would assume that organisation comes easily to me- in fact the opposite is the case but I have learned strategies over the years that enable me to have a well functioning life, successful career etc, and some of those strategies probably look like being hyper-organised (I'm always early, I track my finances religiously, I'm the person who carefully transcribes all the dates from the school email into her diary the minute she receives them etc etc)- sounds completely square but I know from experience that I have two options- stick religiously to the strategies that work for me or else live in chaos. No middle ground. It sometime annoys DH that I always want to deal with everything the minute it crops up but that's because he doesn't really understand that, if I don't, I'll never deal with it.
I mention all this to say that, just because someone doesn't appear to be struggling, it doesn't mean that they haven't struggled or that they wouldn't sympathise with you. Your post really chimed with me despite my life now being very different.
I would suggest the following-
-talk to your doctor about medication
-the ADHD chatter podcast someone mentioned is very good and might help you feel less alone
-There is good evidence that body doubling can help with focus and procrastination. The Dubbii app is pretty good but I think there are others too. It's basically having a video of someone on your phone tidying the kitchen (or whatever) while you tidy the kitchen, and they also do livestreams where 50 ADHDers tidy their kitchens together. Sounds ridiculous but it does work!
-a boring one but the ordinary things of a healthy life really do help with dopamine regulation- exercise, time outside, a balanced diet etc. I know that it's hard to make a start with any of this when you feel unregulated - can be a vicious circle- but to the extent you can manage any of it it would be time very well spent. I still have days where I feel unregulated (I call them troll days) and just want to sit under a blanket and feel shit.
-have you read up on rejection sensitive dysphoria at all. You sound really down on yourself and I wonder whether there might be some of this at play.