It's always difficult to say as to whether one has one disorder or another. In my experience, psychological diagnoses are generally extremely subjective (psychiatric diagnoses are more scientific, but far more difficult to some by), and one is often at the mercy of the preferences of whatever individual is diagnosing them. There's far less science involved in psychology than the profession would like us to believe.
It is my sincere belief that as more is learned about the brain and how it works, we will find that there are a number of different disorders that fall under the umbrella of what we today call "ADHD" (look at the name: "Attention Deficit Hyperactivity Disorder," this is named in relation to the effects, not the cause; it's akin to calling pain in your arm "general appendage pain disorder," while there are several different reasons your arm might hurt).
There are a number of issues that lead to ADHD-like issues, including but not limited to: Depression (Dysthymic Disorder), PTSD, BPD, Brain damage, GAD, OCD, etc.
The point we're at with ADHD is more about treating symptoms than causes, per se . . . sort of like taking Acetaminophen for the flu. As such, if you're finding that you're getting sufficiently positive effects from medication, it's not as important as many may think to get specific diagnosis.
All this is not to say that you shouldn't try to refine your diagnosis, just go into it with the understanding that three different mental health professionals will potentially give you three different diagnoses for the same symptoms. Absolutely consider looking to meditation or other sources to learn mental discipline, organizational skills, motivational skills, etc. Skills have the potential to increase your ability to function both with and without medication, though understand that medication may help with the ability to learn these skills.
There, I probably confused you more than ever. I do hope you find some value here, and hopefully you find a strong footing in your quest to explore your issues. Best of luck.