T.,
I'd highly recommend cutting all dairy out of his diet to see if it helps. Obvious dairy like milk, cheese, yogurt and hidden stuff in foods (you HAVE to read the ingredients in everything). Milk intolerances/allergies are hard to detect but common and usually untreated. Give it a month. It you don't see improvement within a month (assuming you've actually eliminated all the dairy from his diet), it isn't dairy. But I'd be really surprised if eliminating dairy from his diet doesn't dramatically improve his problem.
Alos, if you are in Las Vegas, call Nevada Early Intervention Services. They will evaluate your son and provide services (such as speech therapy) for free and they come to your house. If you aren't in Las Vegas, there should be a similar service where you live. My son has autism and he received services from EI until he was 3 and then we transitioned to services through the school district. Both programs provide services for all sorts of developmental delays, not just autism. You want to check out all of the free services first. We are paying for private speech therapy for my son to supplement what he's getting through the school district and it is $120 a hour. Private services are expensive, insurance coverage is iffy (ours won't cover anything they consider 'developmental') so get all the free services you can and then fill in any gaps with private services.
Good luck!
T.