This sounds like a beginning of a stomach flu.
Vomiting and fever may or may not occur, but diarrhea almost always occurs.
The illness may develop over a period of hours, or it may suddenly start with stomach cramps, vomiting, or diarrhea.
The symptoms are most intensive during first three days.
The most important thing to avoid vomiting is to rest your stomach and intestines.
First, have only small, frequent sips of liquids, and, later when you have not vomited for several hours add soft bland foods.

Do you have some of these additional symptoms: mild fever, fatigue, chills,loss of appetite and muscle aches?