19 month old with "expressive speech delay"...worried..

So, my 19 month old is not talking at all. He says "Ma ma ma ma" and "Da da da da" and that is it. He babbles a lot but no words and he doesn't know that I am "Mama" and his dad is "Dada". If you read my last post you'll see that initially I was concerned that he was developmentally behind because he refuses to eat a lot of foods and I was worried he wasn't getting proper nutrition. Well, since then we have made great strides with the eating so I am no longer worried about his nutrition BUT the dr. says that while he is not worried about his mental and physical development he said that my son DOES have expressive speech delay. He said I need to read to him 3 times a day and he wanted to see me back in 6 weeks. He kind of acted like it was not really a big deal but after reading up on it, I'm a little worried. And the fact that he wanted to see me back so soon didn't help put me at ease. I feel like it's a bigger deal then he made it out to be. I guess I'm just being a worried mom but does anyone have any insight? Has anyone experienced the same issue? I have been reading to him as instructed and he seems very interested in the books and babbles along. But what if he still isn't talking in 6 weeks? Then what? Thanks in advance for any light you can shed!