I am curious. Why would stomach issues cause post nasal drip? Wouldn't it be the other way around? Isn't 99% of nasal infection due to fungus, even according to the Mayo [hold the mustard] Clinic??
Or is post nasal DRIP different from a nasal infection?
Yes, the majority of sinus infections are fungal, which is why antibiotics rarely work for sinus infections.
But post nasal drip is not always from a sinus infection. Any irritation to the sinuses can cause them to release fluid in an attempt to flush out the irritant. With acid reflux some of the acid can get in to the sinuses either as a liquid or vapor. Either way this can irritate the tissues causing them to release fluid.
Another factor is stimulation of the vagus nerve by the acid's irritating effect that can also cause post nasal drip. Ever notice that when you sometimes take something intensely bitter than your nose tends to run? This is from the vagus nerve stimulation.