I was sick for weeks after coming back to the states...and we had bottled water and cooked food at the very best places....no street eating.
Being in Mexico, not just consuming goods imported from there... a whole different story. Montezuma’s revenge.
You need to give your immune system practice. Whenever I go overseas, my first order of business is to eat the food and drink the water. I'm talking straight out of the tap or whatever ditch they drink it from. Food carts along the street, no worries.
It isn't pleasant at first and I've spent more than a fair share amount of time trapped in the little boys room, but I'm at the point now where I rarely get sick and eating foreign foods/water doesn't do much more than a day or so with an upset stomach, if that.
What actually messes me up? MSG and all the garbage "we" put in our "food" here.....I've cut out all the fake food from my diet about 1 1/2 ago and I've felt better ever since (I don't buy into the organic fad, I just want my food to be food and not a chemistry set).