Really worried about my 16month old. Any advice will help

HI
I have two kids one is 2 1/2 and the other is 16months. And I'm currently pregnant. I have recently been stressing out. My 16months old is not communicating very well at all. He rarely says momma and daddy. He says bye bye and sometimes night night. He knows how too high five and fist pound. But he doesn't seem too focus as well as he should be. I have his check up in February but thinking about making one before then. My 2 1/2 year old picked up things a lot quicker than most his age so I never had this problem before. I'm just worried idk if this is normal or not everything ive seen online makes me feel like it's not normal. How can i get him too start communicating better and learning things quicker. Any suggestions would be great. 

I will add tho he knows more than he's showing he just doesn't really talk. He knows who i am and who dad is and he knows ball, bottle, dog etc but he just doesn't say the words.

Thank you