with the possible exception of herpes or syphilis, either of which should lead to a lesion and certainly not to the burning sensation you describe. Furthermore, nausea,
vomiting, diarrhea? - no way from the exposure you describe. Remember, you were
in Mexico from which many return with nausea, vomiting and diarrhea. As for your specific questions:
1. Symptoms of most STDs typically occur within a few days, sometimes as soon as 2-3 days after exposure.