The left side of my stomach hurts, what's the cause?

Many possibilities: A simple tummy ache with symptoms like nausea, vomiting, or diarrhea, whether at home or traveling, may be from a virus infection, bacteria infection, or contaminated food. A normal person, not pregnant, not on medications, usually recovers easily. Taking a Pedialyte popsicle or 2-3 oz of Pedialyte hourly, plus drinking/eating little else, may settle things down. Otherwise, a Dr. should evaluate.