PLEASE get him therapy!! I am a Speech-Language Pathologist. He should be putting at least 2 words together, "mommy go" fpr example. Get in touch with Early Intervention/Department of Developmental Disabilities ASAP and if you can pay out of pocket, have him evaluated by a Speech-Language Pathologist. At two year, nine months old, contact your local school district to have him evaluated for special needs preschool services. They will screen and/or evaluate him in all 5 areas of development - communication, motor, cognitive, self-help, and social.
Keep doing what you are doing. Always pair the sign with the verbal word. You did not do wront by teaching him sign - he is communicating with you and that is what's important. does he make choices? For example, if you say "do you want an apple or banana?" Does he point to what he wants? Always give choices for snacks. Play with him to model vocabulary and how we use words.
I wish I could slap sense into every pediatrician who has told parents to wait.