My son was also diagnosed with Autism last year. He is three years old. The doctors told me that he was on the low end of the spectrum but with therapies he would go up the spectrum, such as Aspergers. My son has not, he has only gotten worst. He says "no, bye and sometimes hey".

Unlike your son, he does not understand what is said to him. So maybe that is a good sign for you. The doctors told me that people with Aspergers are able to more "normal" lives (I hate that word "normal" but that's what they said). We are still hoping that there will be some progress with my son.

I know this is hard to go through. The doctors don't tell you much, so you have to do much of the research yourself lol...
Hang in there!! I wish you all the best of luck to you and your son!!!