My 2 Yr Old Doesnt Talk

When he was 8 mths old he said kitty cat although it sounded like kih kah. then aruond 12-14 mths he said byebye, but other then that i havent noticed a real word, sometimes he says stop it, but he says it over and over a few times. he has said puppy before a few times but thats it, and i read by age 2 there vocabulary should consist of like 50 words and he really doesnt even use one . sometimes he says dada, but again most of the time its repetetive. He also throws tantrums alot. when he doesnt get his way he will lay on the floor and bash his head on the floor or hit it on a table or stick his fingers in his mouth to gag himself, i ignore it in hopes he will stop but so far no luck there. He understands things, like i ask for a kiss he gives me one, i ask if foods yummy and he smacks his lips , i ask him if he wants to take a bath and he goes right upstairs to the bathroom. But he doesnt talk, he has his own language that he bables in sometimes though. He goes for his 2 year checkup next week, im wondering should i bring this up with the dr and what should i ask to help him out?