Possible Autism in 2-year-old?

My son is 27 months old, he says about 20 - 25 words and he points occasionally, but almost always as a mimicking behavior. He can pretend play and he seems bright and able to learn. He is very strong-willed and gets very frustrated when he doesn't get his way. He babbles a lot, but primarily communicates through pulling me to what he wants and guiding and manipulating my hands, as well as screaming, and crying. Lately I have been encouraging him to use words to communicate by ignoring his requests until he attempts to use a word, still it takes many many attempts to get him to speak and again he only repeats the words we have just said. His pediatrician referred us to an audiologist and his hearing was normal. Next we will see a developmental specialist, but that is 7 months away. Should I be concerned that my son is autistic? If he is, is he likely to regress? Could something else be causing his language delay?