Hi: My son was not a big talker when I enrolled him in daycare at 22 months. There was a kid in the class who was 2 months older and talked in full sentences. Talk about intimidating! The kid freaked me out! So I got an eval done by a private speech therapist, and I was told he had severe speech delay and needed therapy twice a week. She charged $50 per session, and she never even spoke to me to ask what he was like at home. After a half hour with him, she claimed he didn't follow 2 step directions, that he didn't know body parts, and that he didn't make eye contact. In his class, he did all of those things, and at home, he did as well. Plus, he is shy around strangers.
In my gut, I knew she was wrong and just wanted the money. $400 a month is a LOT OF MONEY for a total of 4 hours a month. How much more could she do with that time that I couldn't do in many more hours of interaction? Why didn't she talk to me about tips for working with him at home? Besides, his classmate who spoke in sentences was the one who was off the curve, not my normal kid! I really let myself get intimidated, which I found out later, pretty much all the other parents were, too.
Anyway, if your gut says that there is a problem, and he's not improving, then get an eval from the public program where they're not out to pad their pockets. And ask them what you can be doing, too--a speech therapist is not the magic bullet....it's the work you do at home to reinforce it that will help him.
My son was ahead on all other development areas, just slower in speech, but his motor skills and facial muscle development are normal. I was enabling him not to speak. I stopped that, cut out the TV, read more to him, played with him, and noted improvements. When I actually logged how many words he had, it was over 200. He is now just over 2.5 years old, he is potty trained, understands everything I say to him, has many 2-word and some 3-word sentences, says the letters of the alphabet, can count to 13, says "thank you" and "please" without prompting...in other words, he has come around and enjoys talking. Interestingly, potty training also really boosted his talking.
One thing I did that therapists do to help improve the words he already had was to look at him when I speak and have him look at me. He would watch my mouth as I said words, and then his clarity improved. So look at your kid when you're speaking, slow it down a little, and praise the effort.
Good luck! You're the mother, you know him best!