I was also diagnosed around 19 years of age and Adderall/Adderall XR was the first medication I ever tried to manage my ADHD. I feel you completely.
You could be going through the *honeymoon phase* where you experience yourself as a totally different person. It wears off for most people and the key, from my understanding – is not to chase the “good feeling” but rather to objectively observe (over a period of time) if your symptoms are getting better. It could also be that you are now seeing the world through the right pair of glasses.
After a month or so, like mentioned above evaluate (along with side effects, if any) how things have improved (compared to pre diagnosis and treatment). Are you being more productive? Are you calmer? Are you able to focus more? Are you less reactive and impulsive? The list of symptoms is individual to you.
It’s a journey – think of it like a marathon. For me that’s hard because I want everything to be fixed NOW.
Now, I am again on a new journey on a new medication. Being as patient as humanly possible :). ADHD human. Ha ha.