I know that many parents have the same question as yourself. First, please have your child seen by his/her physician. They are often well trained in this area. Second, please contact your local school district and ask (in writing) for a meeting with the early intervention team of specialists. (Do this especially if your child's physician expresses concern, as well). Specialists in the area of autism spectrum disorders will look at a child's interaction with people, language development, and overall attainment of developmental milestones.
I have listed below many excellent websites that have the outlined the "red flags" for the Autism Spectrum.
I can hear the concern in your voice. I have done much research myself on autism and I would like to refer you to this website. It is part of the Mayo Clinic research on Autism and I highly recommend its content. Here it is:http://www.mayoclinic.com/health/autism/DS00348/DSECTION=2
I hope this has been of service to you. After reading it if you believe that your child may be exhibiting signs of autism, please make as appointment with your Primary Physician for further investigation. If I can be of further service to you, please do not hesitate to reply. Good Luck, Dad!