The most effective methods of treatment for ADHD:
* Medication
* Exercise
* Healthy diet
* Healthy consistent sleep
Is it possible that you weren't just unhealthy? Is it possible that diet, exercise, and sleep had exactly the positive effect that they are generally expected to have?
I say this not to reinforce the "maybe" of your own personal ADD/ADHD diagnosis, but to open the door for empathy. You may indeed have been misdiagnosed. You may have a more mild case of ADHD than the mean/average case. You may have a relatively severe case, but experience significant enough relief from your current diet, exercise, and sleep to adequately manage it. Whatever the case may be, I want everyone here to know that it just isn't enough to say, "Just be more healthy." Life is more diverse and complex than that.
The primary effect of ADHD is "executive dysfunction". If the best treatment for ADHD is to eat healthy, exercise more, and get consistent sleep, we must still recognize that that very treatment itself exists behind a wall of executive dysfunction. Even if "healthy lifestyle" is enough, we still need a way to bootstrap it.
It's incredibly normal for anyone with an unhealthy diet, lack of exercise, or lack of sleep to struggle changing any of those things. Someone with ADHD literally has a disorder that makes it incredibly difficult to even get started.
While medication has an immediate and direct benefit, getting through that metaphorical wall to the rest of treatment is widely seen as the primary utility medication provides.
---
Whatever your situation is, it sounds like you managed fine without medication. Lucky you. For a lot of us, life just isn't that simple.
When I try to eat my vegetables, I can put them on a plate, hype myself up for them, and then sit staring while my brain shuts down. I am God, and broccoli is damned. When I decide I want to exercise more, I can get dressed, go outside, even get inside a gym, and pace around the weights or the treadmills, or the swimming pools, and get lost deciding what to do, while my brain screams, "I know! leave." When I decide I want to get to sleep on time, I can lie in my bed, breathe deep, relax, start thinking about more things than I can count, while the amount of hours and minutes slide right off the ledger.
Medication doesn't solve any of that, but it makes some of it possible.