Please help me with imposter syndrome

Every time I start taking my medication I also start believing after a few days that Im just lazy or dump(even tho i have an high IQ) and that i dont have ADHD since i believe that i somehow managed to get misdiagnosed. Beacuse i feel like im productive enough. Its my third day and i already feel anxious when it kicks in. My head feels quiet but im not sure If im making it up or not. Its almost like i feel worse on them? Its my third day tho so i should wait it out a bit. I feel like a methhead in class when it kicks in or wears off and i start getting so jittery. I aslo had a panic attack today and it affected my work badly. My concerta expirience is quiestionable. My first time taking them was while i was still vaping and oddly enough thats the time were my mind was the calmest but my body was suffering and i was loosing a ton on weight. Coffe used to make me sleepy and tired before being medicated. Now when i take 2-3 month brakes off this pill coffe sudenly makes me awake and sometimes even anxious. My resting HR on meds is 120 wich i find extreamly anoying since i cant do anything without it spiking and feeling out of breath constantly. Im already on 18 mg the smalles dose and i cant go lower than that.