M.G.
If he can hear a dog bark, and say "dog" that's a good sign of his hearing. Mine couldn't do that at that age. He ended up with tubes in his ears.
My son's hearing was affected due to fluid, and his speech was affected. It sounded off - so he had words, but they didn't sound right. They sounded 'vowely' only way I can describe it. So 'ball' was like 'baaawwwl'.
I could say his name if he was turned from me, and he wouldn't turn around.
So if your son can hear his name if he's not looking at you, that's a good sign.
However, hearing can be muffled just from a cold. That can delay some kids' speech by a few months.
Some kids just take a break from speech and work on something else. That was my nephew. He had words at your son's age, but didn't start stringing them all together until 2 1/2 then you couldn't get him to stop talking.
If he's had colds, ear infections etc. then you could look at having hearing tested and a visit to ENT, otherwise, I'd trust your pediatrician.
ETA: Reading the other moms' advice, I too would suggest trusting your own mommy instinct. We did, and worked with our pediatrician. If you don't feel you can trust your son's, then you might want a second opinion.