I have stomach ache, diarrhea and flu-like aches and pains with bad headache; is this just stomach flu?

Most likely flu: With muscle aches, sore throat, runny nose, headache and fever - sure does sound like the flu. Good old rest, fluids, and tylenol (acetaminophen) should help. If the fever lasts more than 3 days, belly pain is getting worse, have blood in the stool, or you can't keep any food down, i'd see your family doctor. Hope you feel better!

Probably, but....: These are typical viral illness symptoms, in which case they will resolve within a week or two. General measures include drink lots of clear fluids, broth, tea, water, ginger. The bad headache is a bit worrisome, but the most common cause of that is dehydration (those with chronic ha--drink 60 ounces clear fluid daily: watch). If ha is severe or 'worst i ever had': see doc immediately.