Having ADHD doesn’t do anything to your capacity/ability to think critically, perform complex mental tasks, or solve problems. It’s about your brain’s reward-handling circuitry – it doesn’t quite work right in ADHD people, and that is what drives the behavior and concentration issues. Stimulants more or less make the reward (dopamine) circuitry operate normally. I’m also very good at those things, but often can’t be bothered. Sometimes, though, I’ll get really into a thing and perhaps spend three days doing math to figure out how to properly map a remote control joystick to a robot’s weird steering system that the joystick isn’t really designed to control, and then learn enough C syntax to program the math into the remote control and sensors and stuff so I can drive the robot with the remote control. True story.
It seems like you are one of the lucky ones in that you were able to develop good coping mechanisms and excel at your studies. Mine were maladaptive, and despite getting myself into a very good university, I barely got out. I always got “but you’re so smart! Why don’t you just apply yourself?” It was insidiously difficult to apply myself, for reasons I wouldn’t really understand until I got my diagnosis at 25 and learned what ADHD was really about.
If you’re succeeding but feeling mentally exhausted, you’re probably compensating more than normal people, who’d be able to stay on top of things more easily. Don’t be afraid to try the meds – since you’ve already been doing so well without diagnosis or treatment, just think of how far you’ll go with it. 🙂