I goo gled some of the symptoms in the search engine to see what would come up. First was hidden food or chemical allegries and then Lyme Disease.
I know they have ran plenty of bloodwork but testing for Lyme at some labs are hit or miss. Just because it is negative doesn't mean your son doesn't have Lyme. There is a special place to send the blood work off that know how to test it. I know your son is only 4 but it is possible to be bitten by a deer tick and not know it. You could go to the Lyme board to find out about the lab. I know there is some type of infection or inflammation going on.
I know what it is like to be treating badly by doctors. Since 1991, I had to hound my doctors to give me a ME/CFS dx 1994. Now, as of 12/06 I have MS also. I am so sorry that you have to endure anything like that and watch your child go through this without any answers. I reared two sons and I hated it when they got sick.
I encourage you not to give up. Keep taking him to doctors or specialists until you get a firm diagnosis. I would also keep a journal with dates and durations of symptoms and any new symptoms of your son that could be helpful to the doctors in his diagnosis process.
I wish I could have been of more help. Maybe the others here might
recognize something else. I did look up ME/CFS it did state that under the
age of 10 it was most unlikely for the child to have it.
I will keep you and your son in my prayers.
God bless you,