I have been looking in to Autism/Aspergers & sensory processing and I believe my eldest DS perhaps has this and has been wrongly diagnosed as ADHD his whole life

My son has NEVER been able to concentrate properly. On medication for ADHD (dexamphetamine) he made some improvements but did still complain that he found it difficult when all the kids were talking around him and he was trying to do his work. He also has extraordinarily sensitive hearing - he could hear my mobile phone when it was on silent, just by the vibration, when in the car with music playing. He can also head the high frequency dog alarm things. Because of his sensitive hearing, his problems were obviously just put down as ADHD by the pediatrician(s). I remember a friend who's son has Aspergers telling me to take DS1 to her sons pediatrician as DS1 was doing similar or the same things as her DS. I never got around to doing it as at the time I was a working & studying single mum and the pediatrician was over 500kms away.

Considering my DS is 17 next week, where would we go to in order to get a diagnosis at his age? Is it too late for him? What can we do and where can we turn to from here?