S.W.
Hi D.,
S. here, mom to a son who's 7 and girl who's 2. First off, BREATHE!! You are smart to be checking things out and not waiting too long!
Have you tried sign language? Even kids who are developing 'normally' can benefit. It helps them have a language before they get too verbal and thus cuts WAY down on frustrations and tantrums. There is a great series called 'Signing Times', the show comes on PBS and you can also check them out at the library usually.
Another thing to check into is ssyour little one my have some food sensitivities that are causing behavioral problems. I have just been reading about this on a yahoo group I belong to, its called APVirginia, you could join it and look up the conversations. There are some super smart moms on there who have done tons of research.
Good luck to you! Hang in there!!