I know you may have a diagnosis of autism, but frankly, it sounds as if your son could have suffered from some type of hypoxic brain damage related to the tonsillectomy. Autism would show up way before the 4th year. See a neurologist who specializes in brain injuries and access his medical records from the surgery, if possible. I was a Certified Registered Nurse Anesthetist for 20 years and I know what hypoxic(lack of oxygen) injuries look like. Good luck.