I would have to say that if none of the meds show results, and he has tried every med, at every dose, for the required amount of time( 2-3 weeks), then it is either Not ADHD, or he has another comorbid that must be managed before the ADHD meds can work.
A child may HAVE ADHD, but it is not what they ARE. Never tell a child they ARE ADHD.
Your child may not have ADHD or may have it coupled with some other disorder. (Like Dyslexia) I am not a doctor but I have worked in the special education program at one of our city schools, which
I agree with the others. Sounds like it might not be ADHD, but something else going on. I would definitely consider a fresh opinion from a different specialist to make sure your son gets on the right track.