You need to see a specialist

At least you should call your son's PD and talk about your concern. PD asks about baby's language development at 12 and 15 months visit. If it was my daughter's PD, she would suggest to see a specialst quite a few months ago.

It seems to me that your son did not reach the development mile stone. First, you need to find out whether your son is physically fine (like hearing, able to make noise). If he is fine physically, then you should probablly start language therapy.

Don't worry too much. You should transfer you worry into action. Sooner you seek help, better the outcome.

Your son might be perfectly fine, but you need professional advise and diagnose.