Your story is heartbreaking - I am so sorry for all of the stress you are under.
I assume that you are posting here because of a previous diagnosis or suspicion of PANDAS or PANS. Just in case you haven't seen the workup recommended at pandas physicians network, scroll down to section "III Workup" at this link: https://www.pandasppn.org/seeingyourfirstchild/ . This is not a really long list (like for example, Dr. T's), but a very basic one, and one that a doctor not expert in PANDAS/PANS could respect on account of the board of expert doctors behind this website. At any rate, beyond the basic checks for strep, there is a recommendation to check for heavy metals. That part is worded in a funny way - it's called poisoning, but it's also called a non-infectious trigger. At any rate, I know of a child that had excess mercury in her blood (and hair), and her PANS symptoms did actually improve greatly when they got the mercury level down. It really does seem to act like a trigger. I have heard aluminum as another that possible trigger that you could consider requesting to be checked.
Have you ever chased yeast as a trigger?
For your son, though zith is good, you might consider getting a different abx, as recommended (after 14 days if no improvement) on the second page of this link: https://www.pandasppn.org/wp-content/uploads/PANDAS_Flow_Chart.pdf .