AMYHUGHS: I urge you to look into testing again and to further investigate the definition of autism. You are definitely correct that the autistic spectrum is huge. But there is a precise, clinical definition of autism. A person has to meet very specific requirements in three separate categories to be labeled autistic.
My DD is on the spectrum but does not, by definition, have autism. That, however, does not mean that she does not need therapy and intervention. Pediatricians are NOT the best ones to diagnose autism. Neurologists and psychologists trained in autism are the specialists. I found mine through my school district and the state early intervention program.
Speech delays and flapping are two signs of an autistic spectrum disorder. You can't lose anything by getting him tested. You can only gain either peace of mind that he is not on the spectrum or peace of mind that he will begin receiving help as soon as possible.
Best of luck to you!
I read through this entire thread with interest and just needed to echo this!!!
I have a 3 y/o autistic (mildly affected) son and an 18 month old son. My 18 month old son has been receiving ABA thearpy for 10 hours/week for the past month due to what I truly believe is *just* a speech delay. However, since his older brother is autistic, we've adopted a very cautious attitude regarding our youngest. He is EXTREMELY strong willed and stubborn, even at this young age, which worries me. He occasionally stares into space and does not respond unless I call his name repeatedly (sometimes). Other than that, he does not seem autistic to me. He, at this time, definitely does not qualify for a diagnosis based on the criteria needed. He is, in most respects, the complete OPPOSITE of his brother, both in personality and in how he behaves so much more like a "typical" toddler. BUT, this does not mean he is "typical" or "normal" or "just quirky". There is nothing to lose from getting Early Intervention services. If your child turns out to be completely fine, you've lost nothing, the services are free. The evaluation is free. If not, you got a leg up with starting early. My oldest son began speech therapy at 19 months. He is now in Special Ed preschool and is doing SO well, and I don't even want to think about how he would be if he had not begun therapy when he did. At times, I forget he's autistic, because he has improved THAT much...
If I had waited until the pediatrician noticed that my oldest son needed to be evaluated, I'd still be waiting...you have to remember, pediatricians see your child for NO MORE THAN 15-20 min at a time, in a setting that, frankly, most children do not like very much. Unless a parent speaks up, the pediatrician will have no idea of what a child REALLY is like at home. I had to straight up ask the pedi for the number to call for Early Intervention services, because I had a gut feeling about my oldest son. She is now on the same page with me regarding my youngest...we are BOTH being very cautious where he is concerned.
If a SPEECH THERAPIST thinks your child may be autstic, LISTEN TO HER!!! These people work with kids day in and day out, they have seen a LOT. Don't blow her off. My older sister teaches 1st grade and she has kids in her class EVERY YEAR who she suspects may be autistic (at least on the spectrum) and the parents have NO CLUE, when she brings it to their attention.
I'm not trying to badger, but really, there is nothing to be gained from being in denial. Plus, a speech delay is enough of a reason to qualify for early intervention services. Get in now while your child is young. You don't want to end up having to pay for these therapies out of pocket when he's older (it's SUPER expensive and not usually covered by insurance).
In response to the OP (and subsequent posts):
My son, 3, is autistic (mildly affected). His diagnosis did not come as a shock to me. I was convinced he was autistic from the very early months of his life. I do not feel any vaccines in particular caused his autism. I believe in the genetic element. Upon further research, in fact, I believe my father may be on the spectrum, as well as my younger sister. My husband has OCD and my family has several members who are bi-polar. There is something amiss in our brain chemistry.

My son received the MMR vaccine at 12 months. He was exhibiting unusual behaviors by 9 months.
My other son, 18 months, is not talking yet. He was a month premature, and developed his gross motor skills about a month behind where he should have (which was expected). He is very social and does not exhibit troubling behaviors. He has been vaccinated on a spread out schedule, since the his pediatrician agrees with me to proceed with caution where he is concerned. My pedi's stance on the vaccine link is up in the air. She does not personally believe that the vaccines cause autism, but she also won't rule it out until they find out definitively (if they ever do) WHAT triggers it to develop. She sides with parents on how they want to proceed re: vaccinations. My son was just in yesterday for his 18 mo checkup and I told her I still want to hold off on MMR. Her response was: "I don't blame you." I will probably wait until he's at least 2, possibly 3. My "gut" feeling on him--he's not autistic, but I also have a gut feeling that something is not right.