Even though speaking few words may or may not be a sign of autism, we highly recommend having your child evaluated by a pediatrician and a licensed speech-language pathologist. This is especially true if your child has not received a speech, language, and hearing screening.
A three year old who speaks few words may (or may not) have a speech/language delay, a hearing disorder, or a variety of other issues. Or, your child may not have any disorder or developmental delay at all. Because offering a diagnosis online isn't possible through this forum, we again strongly recommend to have your child seen in person by professionals so that you may have a better idea of why your child speaks few words.