Genetic testing
If your insurance covers it, you should consider getting a genetics workup, ideally through a geneticist. Some of the common tests run on children with ASD are MTHFR, Fragile X, Rett Syndrome, Wilson's Disease, mitochondrial dysfunction, Chiari 1 and PON1.
If your insurance covers it, obtain metabolic and mitochondrial workups as well. Your pediatrician may need to give you a referral for these.
Your insurance should cover these tests to rule out any underlying issues which may affect treatment or therapies.