M.,
There are "lots" of different "symptoms" of autism, but one of the biggest "symptoms" is the change in smiling and interacting. My 2 1/2 year old son has been diagnosed with a form of autism, and I have had to FIGHT to get the dr's to listen to me. Fortunately, we now have insurance that does not require our primary care provider's referral to specialists (aka, "self-referring" policy), so we made an appt with a neurologist who specializes in Austism Spectrum Disorders (ASD).
I agree with Stephanie...while babies go thru a lot of "stages", "hamming it up" for the camera or not, is NOT one of them! Your son is very young to be able to get a correct diagnosis on these disorders, but I would start paying attention to changes such as changes in eating habits (is he getting very "picky" for particular foods?), speech (losing words....my son has a limited vocabulary, and does not say very much, which he should be saying more than he does). Our son expresses himself mostly by throwing MAJOR fits when he doesn't get something (more so than a normal 2 year old), or laughing "hysterically" when he is extremely happy, which is really fun to watch. This usually means we have to GUESS at what he wants, which is frustrating for all of us! When he was a newborn, he would *scream* at the top of his lungs when his diapers were being changed, or when we put him in the tub for his bath (these are signs of his condition).
Anyway, it's too early to "freak out" about his behavior, but I would start paying attention to things that just don't seem "right". I would also make sure that each of his vaccinations, including the flu vaccine, from now on do NOT contain Thimerosal, which is a preservative. As I've stated on other postings, I don't believe it's the vaccines that are causing austism, but the preservatives in them (backed up by research I've been reading).
Feel free to contact me anytime if you notice something "peculiar" and you want to talk about it. My phone # is ###-###-####, and my email is ____@____.com.
Blessings to you and your family!
~J.~