Our 8 year old daughter was formally diagnosed with Autism when she was 3. She is high-functioning. Extremely smart, but her social skills are lacking. Look into all the therapy you can possibly get, you should qualify for some of it free. She got speech therapy starting when she was 2.5, and once she got formally diagnosed she became eligible for inclusion-therapy and occupation-therapy. Positive results from both. The therapists can even come to your home or school.
One important thing to know is that Autistic people see, hear, and feel things differently. Google the "Arthur" cartoon episode where he meets an Autistic school-mate and tell your family to watch it. It will help them understand what your son is going thru from a sensory standpoint.
Temple Grandin is an expert on Autism and is actually Autistic herself. She is a PhD. Her biographical movie is very interesting and will hopefully help you gain more understanding of how Autistic people tick.
Autism has a very large scale. I'm not sure where your son falls on the Autism scale. I am an engineer and there are about 200 engineers onsite where I work. I could probably point to about 3 or 4 of them that I would say are somewhere on the Autism scale, and I'll bet they don't even realize it.
I tell you that so that you will know a diagnosis of Autism is not the end, it is the beginning of your opportunity to give your son everything he needs. Take the time to learn about. Find out what therapies he qualifies for and needs, and get him those therapies.