PLEASE take your son to a developmental pediatric psychologist for an evaluation. Doctors do not know how to diagnose developmental delays, TRUST ME, I learned the hard way. One out of every 166 children born between 1992 and 2003 have been diagnosed with being somewhere on the autism spectrum (they're not all Rain Man). My three year old daughter is somewhere on the spectrum and if I had her tested earlier, she could have received speech/occupational therapy earlier. Developmental delays CAN BE overcome with early intervention, my daughter's developmental psychologist thinks she'll be mainstreamed into a "normal" kindergarten by the time she's 5. She is a new little girl because of all the therapy we get, through private insurance, but if your child has a delay, you can also get services through the State.
It may be nothing, my friend's son didn't say anything until he was 2 and he's just fine. However, for years I listened to all of my family and friends telling me that my daughter would just "grow" out of her behaviors, and now I kick myself for that! I am an attorney and was possibly paying too much attention to my career to follow my gut. I have now quit my job and am a full time stay at home mom. Please take your child to a psychologist, don't be afraid of labels, children can always "lose" their diagnoses, they're not necessarily labeled for life. But if your child has any type of delay, a developmental psychologist will be able to pinpoint it and recommend treatment (non medical, of course). If you treat developmental delays early, your child may never ever have to set foot in a special-ed class when he's older.
Email me if you have any questions. But have your pediatrician refer you to a developmental psychologist -- make sure your concerns are NOT ignored.
Good luck, K.