It really sounds like you should have your child evaluated by a team of specialists including an audiologist. The suggestions from Susie2007 that I see above do seem to be good ones; it is impossible to give a good diagnosis without actually examining and meeting the child and talking with his parents.
A developmental pediatrician or a neurologist/psychologist who specializes in ASD can diagnose him. He sounds very much like my grandson who was origianally diagnosed as PPD but now John Hopkins (Kennedy Krieger Institute) believes he has Aspergers. He has been in therapy since he was 14 months old. He is almost 3 now and is doing fantastically well. Good luck.
Thank you very much for responding! my son is responding well to therapy. He was only seen by a developmental pediatrician and not a team of specialist as you put it. I will try to see an audiologist for him. thank you again!
thank you for your comment. my son was seen by a developmental pediatrician who diagnosed him to have global developmental delay-to consider autism spectrum disorder. are the therapies for ASD and GDD different? anyway, my son is responding well to therapy.