Hi K., I have 3 boys, 4, 2, and 6 months. My oldest was saying everything at 19 months. He was very verbal, easy to understand, and had a very large vocabulary. So it was difficult for me when at 18 months old my 2nd child said only dada and ball. I mentioned it to my pediatrician. She wasn't concerned, said it was probably his personality, or because he was the 2nd child, or that his older brother did everything for him. I knew something was wrong, I insisted on a rewferral for a speech evaluation. I was then referred to Early Intervention. EI sent a Speech Thereapist, Physical Therapist, and an RN right to my home. They evaluated my son, and his comprehension was fine, but his expressive speech tested at the level of a 13 month old. We were lucky, because they unfortunately combine the test scores for expressive languange and language comprehension, and his combined score was too high, and he did not qualify for Early Intervention Services, BUT the RN and Speech Therapist discussed it, and the RN overuled his score, and 4 weeks later he began FREE speech therapy 2X a week in our home. He is now 2yrs and 9 months old, and he just tested at 3yrs 9 month for comprehension and 3yrs 7 months for expressive, but only 2yrs 0 months for articulation. So he is still receiving speech therapy once a week, and we are working on making his speech clearer. So my advice is to insist that your pediatrician refer you to Early Intervention, or call yourself, they provide FREE speech therapy, and will begin before the age of 2.
Once we started meeting with a speech therapist, I started teaching my son some sign language (more, all done, milk, juice, open), and he picked it up fast. Then I took a coffee can, and we decorated it with stickers, and I put pictures in it,(ball, book, bed, bear etc.) and made a game of him looking at the pictures,saying the word, then putting the picture in the can. This rote method of repeating the same picture words over and over again really worked with him. Also, I switched him from a sippy cup to a straw cup, and a regular cup, to help improve his oral motor skills. He couldn't blow a bubble, or blow a whistle. So we practiced that too. He drooled a lot. Every morning his pillow case had to be changed. He is doing much better now. No more drooling, he is talking, and is doing wonderfully.
We also had his hearing checked, which is difficult at such a young age. But what we did find is that he has fluid behind his eardrum, so after 3 hearing tests, my Pediatrician prescribed flonase, so we are waiting it out to see if we can clear up the fluid behind his eardrum, and get a more accurate hearing evaluation. So have your son's hearing checked too.
Even though you said you don't know what "normal" is, trust your instincts. Moms know their children better than dr.s do! Good Luck!