Frusturated with inconsistent vyvanse results .

Patient: I’ve been getting inconsistent results from my Vyvanse. This is my first ADD medication and I started a month ago on 20mgs. Quickly going to 40mgs since the 20mgs didn’t do anything. On the 40mgs i felt extremely motivated to do whatever was needed to be done. I felt alert, happy, Focused and Confident in my self and my work. It was as if the “windshield wipers” were on and i can see and understand things clearly. However the 40mgs lost the effectiveness. And i wouldn’t feel anything, no motivation, no concentration. I would become irritable and little things would get me mad and I would also become distant. I’m now on 60mgs and the first day i felt the desired results as listed above, but Today being the second day, im back to the negative results. Are inconsistent results like this common? Am i expecting to much from this medication? Over all, what can i expect from Vyvanse. I’m a 19 year old male and i weight 137lbs if that matters. Any feedback would be so greatly appreciated.Sincerely, Taylor H.