I’m sorry you’re in so much pain. You’re being very hard on yourself and it sounds like you could use some help! Have you thought about telling all of this to a professional who could give you an official diagnosis and perhaps suggest some resources for you, or medication, if that’s something you might want to try? It sounds like you’re self-medicating, so finding an effective medication might help with your ADHD, and the anxiety and depression you’re feeling as a result of your ADHD symptoms.
Having a diagnosis might also help you to get back on track with school – universities are often able to make accommodations for students who need extra help, like changing the way tests are administered, extending deadlines, etc. If you like what you were studying in Uni and were close to finishing your program, maybe talk to someone at your Uni about your struggles too, and see if they can help you make a plan to get back on track. There’s no shame in taking longer to complete your degree, you just need the right help and maybe some accommodations for exams.
I don’t have ADHD, but I know from experience with other struggles that our problems feel the biggest when we’re trying to hide them from everyone. Being open about what you’re going through is the first step to being able to get help and tackle your problems. You don’t have to do it alone!