I would also advise trying to find a psychiatrist who ideally specializes in ADHD for adults, primary care doctors often don't have the education to fully understand the condition. CHADD (Children and Adults with Attention-Deficit/Hyperactivity Disorder) has a resource guide that may help you find a good doctor in your area, it's how I found mind. Psychology Today also has an extensive website for finding doctors also. My only warning with that is Psychology Today allows doctors to list all the of the conditions they treat, but only allows them to list 3 specialities. You can't search specifically by specialty, so you'll just have to filter doctors who list ADHD vs those who specialize on your own. Feel free to DM with any questions!

I would definitely find a new doctor especially a specialist. Caffeine and sugar can help manage some of the symptoms, for me caffeine in the right doses puts me to sleep and sugar helps me concentrate and lower the amount of brain fog I experience. Plan things you want to do in the day ahead mentally, or written down, so you know what you're supposed to be doing and where to start and then set lots of alarms as reminders and motivation to do the things you procrastinate or move from task to task or break. It also frequently helps to break up tasks into smaller easier to do tasks to make it feel less overwhelming and give yourself breaks and rewards to keep you motivated and to make sure you don't mentally or physically overwhelm yourself. I have to live with incredibly bad adhd without meds so I know alternatives for pretty much every symptom I could find it for.

ADDitude is an online magazine my therapist recommended because I can't have ADHD meds (genetics) and the articles on there have helped me tremendously. Alarms are my best friend to pull me out of a task.

Caffeine is also a stimulant, it may help you focus! My other suggestions are making sure you try to get good sleep (I know that's tough with ADHD, but it helps with the brain fog), lots of alarms to help with time blindness, creating incentives for yourself (if I finish ____, then I'll spend ___ amount of time on my hyperfixation/get myself some chocolate/etc.), and "body doubling". Body doubling is just having someone else in the room with you doing their own thing while you work, tends to help me when I'm trying to get something done I keep getting distracted (even a big mirror could probably do the trick if you live alone, or working somewhere public like a park or library). Also make sure you're not understimulated, that'll make inattention worse, so get fidget toys and/or listen to music (something repetitive or that you've heard a million times works best). Try to remember to eat, (this is something I forget a lot, and not fueling your body makes inattention and brain fog way worse) and try to eat high-nutrient foods when you can, ideally whole foods (meat/cheese/whole grains/nuts/etc.), not "zero-calorie/diet" whatever. Hope some of these help! Also, keep trying for a diagnosis, get a second opinion, ideally someone who specializes in adult ADHD.