My son is 6 and was diagnosed with ADHD when he was 4.
I wouldn't beat your self up for him being "punished" even people that know what might be wrong at an early age sometimes can't always get the school on board to help.
If you don't think the meds are working correctly you might want to talk to the Dr, it's possible that he may need an increase, as kids grow the old dosages sometimes become ineffective.
Don't beat yourself up about not seeing it until now.
I know he has ADHD.
It is quite possible to have ADHD concurrently with an ASD.