you're an individual, so i'm not sure what advise will work for you but
1: if you relate to ADHD posts, you ain't gotta get a diagnosis to use the tips and tricks ppl have posted to help with ADHD
2: if you do have access to a health professional and feel comfortable asking for a new prescription, you don't need a diagnosis to be prescribed non-stimulant ADHD medicine, like strattera or other dopamine-reuptake-inhibitors. hell, if your doctor is cool enough they might get you stimulants without a diagnosis (though there is currently a shortage in the USA, so ymmv)
3. my biggest catch-all tip for ppl w/ ADHD is this: Do it the way you want/need to do it. whatever 'it' is.
If you need to take the cabinet/pantry doors off so you can see what's in there, do it. If you need to store your vegetables in the front of the fridge and not the vegetable drawer so you actually see them before they wilt, do it. If you need music playing to focus on homework, do it. If you need to keep snacks at your desk so you actually remember to eat, do it. If you need to set 16 reminders per day to get your work done, do it. Do it scared, do it wrong. You don't even have to do your best. 30% is better than 0%.
And if you can't do it, that's okay too. There's no wrong way to live your life. Just, you know, live it.