Will Pharmacias in Progresso Nuevo Give Pencillin Shots?

OP: I actually am a doctor, so don't use the old "don't know what I'm talking about" on me.
You've been given the correct information here.
It is up to you, however, to believe and/or follow it.

In answer to your question, you can buy azithromycin over the counter in Mexico if that will satisfy you. And I would predict that you could get a "shot" if you persisted. Please explain to me, though, how a single injection of penicillin accomplishes anything, considering that your followup oral drug is not the same.