A.G.
I would certainly have him evaluated by a specialist. You may also want to check for food allergies or reactions. My son acts that way if he eats something with red dye. I know it sounds crazy, but just a few jellybeans will set him off. It is possible that something your son is eating/drinking could be causing this behavior. I also recommend the melatonin for sleep. A friend of mine who has a son with autism also uses it, and it has been very effective.
What is your son drinking on this liquid diet? Is it sugary juice, or is he drinking something with more substance? Again, too much sugar can cause reactions in kids. (even natural sugar in juice - and something like koolaide with dyes could be especially bad.) I would cut out all high-fructose corn syrup and dyes for now until you find out what the problem is.