T.N.
My son wasn't saying anything at that point. He's 2 1/2 now and is only now saying what your boy says at 20 mos. We have him in speech therapy and it has really helped. Its helped me as much as him I think. Just watching the therapists deal with him and learning from them has been most helpful. He does the loud yelling too. I think because he understands more than he can express, its frustrating. Just imagine how frustrating it would be for no one to understand what you want, and you don't know how to tell them what you want. When my son screams, we put our hands over our ears and say, "too loud". This didn't stop him at first, but it catches his attention, and he knows we will tell him this each time. Now he doesn't scream as often. It also helps to give him a sign for mad or sad. After you put your hands over your ears and say 'too loud', you can then say "I know you're mad" and do the sign. My son always gets mad when he can't have gum or candy. He'll request it and is proud that I understand, but immediately screams when I say 'no gum' or 'no candy'. I tell him I know you're mad (and do the sign for mad), but you can't have any. You'll have to wait" (I also give him the sign for wait). We use this sign a lot as well. This way he know we understand whatever he's asking for, but we have to wait first. Even with signs its frustrating, because there will be something he wants but he doesn't know the sign, he'll try to use his hands to make any sign. We just keep pointing at things untill we get it. When we do, he's so relieved and happy. Then we repeat what he wanted. "You want yogurt", reinforcing communication by telling him with words what he wants. Actually, anytime I do a sign, or he does a sign, I also use the words.
I know this is a lot and still not much, but sign language and reinforcing with words is what they suggest. And leaving out all the little words. Say "more drink" instead of "you want some more drink". Later, you can add those back in.
Good luck, T.