Doc thinks viral pink-eye b/c caught cough from older sister and runny nose. gave eye antibiotic b/c lot of eye mucus. why did eyes improve on erythro?

Coincidental: if it is truly viral pink eye then erythromycin does not effect it. a virus is not treated with an antibiotic. your improvement it purely coincidental or it was not a viral but rather a bacterial conjunctivitis.

Anti-inflammatory: Interestingly, these antibiotics do not only act through microbe-killing action. Macrolide antibiotics like azithromycin, erythromycin and clarithromycin inhibit inflammation. They've been shown to inhibit "messengers" such as leukotrienes, tnf-alpha and interferons to name a few. Thus, there is a therapeutic effect of macrolides in viral infections, but we should not use antibiotics carelessly.