I completely understand your frustrations. While my son isn't exhibiting such "severe" behaviors, we can definitely sense something, especially since his father has ADHD.
I know they don't like to diagnose ADD/ADHD so early, usually waiting until 6 or so. At least that was the advice I was given. So I talked to a few friends with children in the same boat and I'll pass along what they've told me.
Find a developmental pediatrician if your reg one isn't helpful. They are trained in ADD, autism, etc... Here you'll hopefully get a clearer picture and trustworthy diagnosis.
In the meantime, watch his diet. Eliminate red dye #40 and yellow dye, which tend to be in everything, and high fructose corn syrup, again, in most of what we eat. I've been told of great success with this. How much calmer the kids are, and capable of listening and making good decisions.
My son sees his regular pediatrician next month, so in the meantime I'm altering his diet and researching some discipline/behavioral methods that I can use now at his age.
Good luck, I know for many it's a long road, fighting for a diagnosis and then appropriate treatment and educational support.
J.