I agree with Linenup get him tested. Try to do the tests at the full moon ( parasites more active then). I tested negative for an amoeba and then positive when I provided samples at the full moon. The lab should provide 3 sample pots with fixative (preservative)and you take samples over 3 days.
I would discontinue the Kefir until you know the results. Some probiotics for some people can feed parasites. The worsening of symptoms may not be die-off. I recently tried kefir for a few months directly after a parasite course of treatment and was horrified how my health deteriorated.
I had to do another course of parasite herbs which I am just finishing and my health is much better.