Zara,
I've already replied to this on Facebook, but will post my reply here as well.
it does seem to be the asunra causing the problem. I don't know if there is a remedy other than to try a different chelator. It could be an allergy or perhaps a mineral deficiency caused by the asunra. I would suggest having his calcium level checked before changing chelators. [Added here.] You might also consider giving him a calcium and magnesium supplement to see if it helps. Magnesium is very important for the nervous system.