I don't think there is anything to worry about quite yet. I have a friend who's son didn't start really speaking until he was 3 and of course they were worried for a long time. It sounds like your DS is hearing just fine and am sure you would've noticed this a long time ago by him not reacting to your voice when you speak to him. Now, my personal opinion... sometimes they like to scare us with "averages" and we have to remind ourselves that those are calculated from early development and very late development. The kids are all different. My DS is 17 months and he has maybe 5 words, and another friend has one the same age almost saying sentences. You are not failing your son! Just by worrying about him makes you a very caring mom.

My son said four or five words until just after he was two years old.
He did have a whole bunch of his own language that he used all the time.
We used to call him The Preacher because he went on and on waving his hands and pointing his fingers and pacing the floor while he was doing it.
Just after he turned two his language just exploded!
And it wasn't toddler talk either. Some folks who meet him can't get over how well he speaks.
I think he was just observing and practicing inside his head while we were worried he would never talk. He was saving it all up.
Now I can't get him to stop talking sometimes!
Unless there are other things that are worrying you or the doc, your little boy is probably perfectly normal. Maybe even so smart he wants to have it perfect before he does it!
Try not to worry in the meantime.
Enjoy him rambling in his own language.

I once heard someone say also that "boys walk, girls talk" meaning that while other children are learning to talk your little one might be perfecting other skills like walking and climbing and running.

One of my friends that got something really close to her daughts heart like the swing and so she use to take her to the swings and is like swing and wen she sed it she got to go on the swing and get pushed and then from there it went to good like pasta and stuff and so she jsut started that way

My daughter was slow to use her words... She does have mild hearing loss that she was born with, but it seemed to affect her speech more than her actual hearing... Weird I know. She would seem to hear us just fine from other rooms but would speak in her own lingo most of the time. We decided to skip the speech specialist and I just kept up the reading, and I'd have her watch my mouth as I said words... Now she is 4 1/2 and we can't shut the girl up!! She eventually became interested in learning real words. Now you can't tell her apart from any other child!

My baby is 2 and she doesn't talk but she hum songs she like her doctor said that she may not be talking because there are no other babies around her, my two older kids are 11 and 9 so they do not have time they are doing there own thing, anyway we have a speech teather that comes to our house once a week and I have also joined a playdate group that have little kids I hope she can pick up some words. I hope I help you a little have a blessed day!!!!