If not, I would definitely start there, by contacting a
speech-
language pathologist (the local school district is a great place to start, they provide services as early as age 3). They will definitely want to start with a hearing screening, and then evaluate his speech, language, and social skills.
It could simply be a speech/language issue. If his delay is significant, early intervention is vital for him to catch up to peers by the time he needs to start learning to read and write.