Im sorry to hear this, what you all need to do which you may have to get 100% rude to do so, is demand all types of blood tests to be done testing for all forms of cancer etc... demand MRI's to be done, CAT Scans to be done.
I have read a similar story about these symptoms and it turned out the child had cancer.
Im not trying to upset you or make you scared more than what you are.
But you all need to do this, your son's life may be at risk.
I will pray you all will find out whats going on and that he wil get better.