This is very much a Your Mileage May Vary thing. I didn't have a nasty adjustment period at all and I was diagnosed in college.
I've heard this happen to other people too, and it's frustrating, but luckily it also comes with the feeling of clarity that was always missing, and fortunately people around me are supportive. No lasting damage, just "oh yeah I was a bit on edge then"
My dr prescribed Paxil, which did away with that problem.
I'm surprised by that impression as my understanding was that it was "generally accepted" that a combination of therapy and medication was more effective in treating ADHD than either alone.
If you have to chose one or the other, medication will be much more powerful, but the combo is the best. But trying to fight ADHD with just CBT is a massive uphill battle once described to me as "asking someone who needs glasses to see to train their way to better vision"
My understanding is that if you actually don't have ADHD, the medication isn't effective, so if it's helpful there's a strong signal there.
A proper analysis by a psychiatrist would be helpful (and you should share your doubts). But I think if you look at things beyond the "attention" and "hyperactivity" aspects . For example, saying things without thinking, lots of remorse for actions after the fact (showing proper judgement but lack of control), etc. Medical professionals are the best for this, but there's a lot of reading out there that you can check out.