You certainly have many questions but the main point seems to be that you question the diagnosis of autism for your son. You mention that his school has diagnosed him as having an autism spectrum disorder (ASD). Some schools have excellent diagnosticians who are experienced and well qualified to make such diagnoses but many do not. You also mention that there has been metabolic testing that has not come back abnormal. Though many have suggested metabolic abnormalities in persons with autism, metabolic testing is not a valid means of diagnosing autism. In fact, if one were to rely soley on genetic/metabolic testing only about 40% of cases of autism would be diagnosed and this testing would cost well over $30,000 per child (according to tiered pricing offered for genetic evaluations by qualified geneticists). Such genetic evaluation usually occurs following the diagnosis of an ASD. To definitively determine whether your son has an ASD, I suggest that you find a developmental specialist who is qualified to adminster the Autism Diagnostic Observation Schedule (or ADOS). With this test you will have an answer to that question.
Best of luck.