I am going through the exact same thing. My son will be 2 in August and doesn't say even one word. He too, understands us. If we're looking at a book(his FAVORITE thing to do!)when we ask him to point to certain things he does. He loves pointing to things! When he needs something he will take us by the hand and show us whatever he needs. I have a wonderful pediatrician who had us get his hearing checked at his 18 month check up. So, we've done that and it was fine. Not his hearing. We now are starting Speech Therapy. So far, we've only gone for the speech evaluation. Which, by the way, was hard on me. No one wants to hear that their 22 month old beautiful little boy has the speaking ability of a 3-6 month old. However the therapist was awesome and had him doing some new things just by the end of the evaluation. So, we are now going to start him with the therapy as soon as we get the insurance all straightend out. That's another thing, a lot of insurances do not cover speech therapy. We are very blessed to have one that does. In addition to the therapy, we are also doing an Early Intervention program which is run through the state. Since it is through them with grant money, it is free. In that situation someone will be coming to our home to work with him here. Since it's free, it will take a little longer to get him started with it because there's a lot of children using this resource, but at least it's there!! I am just so thankful that there are resources out there to help us.
It's been so frustrating not having him talk. He is the most loving, funny, beautiful little boy ever(I know I'm his mom so I'm probably prejudice but that's my right as his mom!:)
My daughter spoke very early and is actually very advanced for her age so this has been doubly hard seeing the vast contrast in my children. It's hard also not knowing why he isn't talking. His hearing is fine, there's no autism (thank heavens), he is so smart in everything else he does. It's just one of life's little mysteries.
Anyway, I've gone on long enough. I would definitely start out by having your pediatrician refer you to get his hearing tested then move forward from there. From what I've learned, the earlier you start to get him some help, the better off he will be. Oh, I should mention also that both his hearing test and now his speech therapy were done at Tucson Medical Center and I couldn't be happier with their therapists! Very friendly, very competent, very punctual.
If you ever want to talk or just vent feel free to contact me sometime.
Best of luck for both of us!