AS commonly misdiagnosed as either or both OCD and ADD so it is definitely worth getting a second opinion. I wish I could offer you more specific guidance on obtaining that, but we were lucky enough to get it right the first time.
The only other thing I can say is this: when your child's diagnosis is right, you will KNOW it, I truly believe that. It will add up. Things will feel like they've fallen in place. So keep pursuing information and additional opinions until you can acheive that level of comfort with the label. Trust your instincts.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).