What Causes Severe Nausea But No Diarrhea?

Think I have the flu, but severe symptoms happen EVERY OTHER day, (vomiting-severe nausea but no diarrhea). On alternate days I felt almost normal, eating well, working out, etc. . Is this common, or could I be experiencing something else. Temperature slightly below normal even on symptomatic days. First symptoms began on Wednesday 14 Jan.