Could I have Undiagnosed ADHD? How to Find Out?

For my whole life, I've wondered how anyone can study for 3 hours straight, or get more than one main task done in a day. For me, I can only reliably get one big task done in a day (and oftentimes not even that)

If I get up from a task, it means I'll probably not return to it until days later or forget about it. And I'm completely unable to stick to schedules for longer than a week. And I'm only able to start those tasks if I'm not in the slightest distracted or tired.

Last week, I talked to a psychiatrist about my attention problems, which I'd blamed on my anxiety and depression, and lack of a consistent sleep schedule. He recommended I try 10mg of IR Adderall once per day as needed.

Today was my first day trying one after a bit of fear and deliberation. I expected to feel amped, but instead- I felt mellow, yet productive. And while I wanted to procrastinate and game or nap, I had the willpower to tell myself no for the first time and keep working. (I was even able to take a break, walk downstairs and get water and still successfully get back to work!)

Is it possible I've had undiagnosed ADHD/ADD this whole time? It's something I want to ask him during our next appointment, but is it as simple as asking to get tested? What is the process like to find out?