Hi M.,
Wow, I am sorry to see all you are going through.
I have a six yr old son w/autism and a 3 yr old daughter with PDD/NOS. I can suggest to you that you get in contact with your local Regional Center, but your Ped. should refer you to a Ped. Neurologist, they usually will test him for auditory issues and lab work for fragile x syndrome too.
From your description, those are symptoms of autism BUT, it must be accompanied with other signs as well. If you go online you can look up symptoms/signs of autism. I remember, reading those and with what felt like a knife in the heart realized, that it did seem my son had autism. It's not the end of the world,though.
My best advice to you is if/when you get a diagnosis, get him help ASAP. Everything you'll read tells and I can vouch for it first hand, that it is priceless and crucial for his development.
I wish you and yours all the best and if you can find it online read a poem called "Welcome To Holland". It's a beautiful,uplifting piece I think about when I get sad about the cards my kids were dealt. It reminds you that life though not what you expected it to be does go on and that you still have a beautiful gift in your child. He is alive, and healthy and there is light at the end of the tunnel.
If I can help any you know where to find me :)
A.