Yes, you need to speak to your pediatrician and get referred. They need to refer your son for a speech and language evaluation. Since he is 3 years old, you might want to check with your school system. I found out a year too late that if I had taken my then 3 year old son to the school system for a speech/language evaluation, I would not had to private pay for speech therapy for a year because my insurance would not cover it (that was $40.00 a session total $1920.00 .) My pediatrian never said anything and the speech pathologist we went to never mentioned it (I don't know if they knew or not).
Our school system accepts kids at 3 years old. He would have been put in what is called an I.E.P. (Individualized Education Program) and the speech therapist would have come to our daycare for FREE. LIVE, LEARN AND INFORM OTHERS!!!
I might have had other services available to me that I lost out on due to my own ignorance.
I would also recommend a referral to a pediatric audiologist (for a hearing evaluation) and a pediatric ENT (Ears, Nose and Throat physician) to make sure nothing physical is getting in the way of his speech production. Your school system may have one, check with them. Many times, the audilogist is in the same office as the ENT so the appointments may be made the same day. I wouldn't have a hearing test and speech test on the same day, your child won't last (it took two sessions for our first speech test due to my child pooping out).
Get your doctor to refer, because many insurances will not pay without a referral from the doctor for these specialists. Also, make sure you have them send the results to your doctor and make sure you get a copy. If you go throught the school system, make sure they get all copies of any testing you have done.
Good luck.