Having my disability questioned.?

Why do they need to know you are autistic?  Do you want them to know, is it to your advantage?  Are there compensation you would  get, you would  need? 

Then go through  your HR department.  Your doctor would need to fill out forms that are submitted to HR giving proof of your diagnosis.

maybe you should get your doctor to write a note about it

I would say so, yes.  Who are they to know what condition you have?  They are not doctors.  I suggest that you get a letter from your doctor to confirm the presence of autism, with their signature or something like that.

I am concerned that this person is likely to bully you in the future, as that is not a normal comment to make at all.  Please contact for help from social services for advice if you are at risk and/or need help with this person.

Unless you can produce documented PROOF that you have an Autism spectrum disorder, then it's not surprising that your bosses think you're lying. And you shouldn't try to use ASD as an excuse to get out of work, unless you can prove that you have it.

Employers are required by federal and many state laws to make reasonable accommodations for workers with ASD's, but the worker MUST SUBMIT written proof of the disability in most cases.

maybe you should get your doctor to write a note about it

If you're so high functioning that nobody can notice you're on the spectrum you can't claim to have a disability.