He most likely has some heavy metals and a virus. The rabies shot replicates the symptoms.
I would give him a tiny pinch of cilantro, 2x a week to gently remove the metals. A smidge of non gmo lecithin. That will help his liver.
An antiviral remedy we gave our dogs was l lysine. Open a capsule of 500mg and give 1/4 of the powder in a ball of liver sausage. 4x a day, for 3 days