I fo not know San Carlos.
I have been only to Bacolod and Dumaguete on Negros.
I live on Cebu, two hours south of Cebu city.
Even small towns have various drug counters.
I do not take any drugs or have any known medical problems,
but many, if not most of the American Expats here are grossly overweight, taking numerous medications, look like hell, but seem to survive.
I did buy some oral antibiotics for an infected scratch, and had no problem getting what I needed.
Most drugs do not need a prescription unless you are buying from one of the big drug chains in the cities.
Most every town has some sort of hospital.
San Carlos is straight east of Bacolod...on the coast...i may be traveling there next year for a visit.