Is this from having had chicken pox?
There is no cure for chicken pox. It gets better on it's own (like a cold or the flu) if you have the chicken pox.
Did the symptoms come on while he was ill, or after?
I'm very sorry the child is still experiencing problems after having chicken pox. This is uncommon, but there are several potential complications that can be the result of chicken pox infection that may explain this child's symptoms: http://www.childrenshospital.org/conditions-and-treatments/conditions/c/chickenpox/symptoms-and-causes
Unfortunately, most of these conditions do not have cures, but can be made better through treatment and therapy. In the link I provided, there are several highlighted conditions. It is not possible for us to know which of these he may have, but if you click on each one, you can get more information about symptoms and treatment options.