We really need to look herbal remedies in this kind of situation. Things like elderberry extract, sassafras root, willow bark, chamomile, etc. Raw honey is good as an antiseptic, witch hazel is a good astringent, garlic can lower blood pressure, etc. My point is that in an extended situation modern medicines may not be available and alternatives are good to have on hand. You can also get antibiotics at the feed store. Look for the fish meds, e.g. fish mycin is erythromycin, etc.
SurvivalNurse has some good youtube vids on these subjects.