Hi, and welcome.
First... this is not your fault.
This isn't a "parenting" problem. It's a child with major challenges. You are not wrong - there is more going on. Doctors won't usually acknowledge that. But...
Has he ever been evaluated by someone other than the pediatrician or family doctor? A comprehensive evaluation would be best - the kind that take 6-10 hours of testing, often across more than one appointment. These kinds of kids need very different handling, and early intervention is almost essential.