What Causes Diarrhea, Vomiting And Abdominal Pain?

With symptoms of severe onset of diarrhea and vomiting, abdominal pain and cramping,chills, headache, and feeling awful (since early Sunday AM), how do I know if it s food poisoning or just a GI bug? I have been slowly trying clear liquids and dry toast--diarrhea continues...I ate out Sat. night but so far nobody else has reported the same symptoms.