Dear ObeyBeautiful, Hello.
As you are on vacation to Mexico, the problem mentioned by you can be due to Travellers Diarrhoea
It result in infection of the gastrointestinal tract resulting in diarrhoea and pain abdomen. Fever
can be due to the infection. Headache can be due to fever or due to dehydration
as a result of diarrhoea.
For relief you should start antibiotic and antiamoebic under medical supervision. Also use Probiotic
You should take proper precautions on eating habbits when on tour.Always take filtered pure water with you.