Both gastric flu can and food poisoning may present with similar symptoms and difficult to differentiate although the former tends to present more with fever, nausea and vomiting while the latter is associated with ingestion of contaminated food that cause cramps and diarrhoea most times.
As far as treatment is concerned, adequate hydration is the most important aspect besides controlling symptoms. In some cases, a course of antibiotics may be required for suspected bacteria infection especially if the fever is associated with blood stain stools.
Avoiding diary products and taking smaller portions each meal may help. Consider drinking fruit juices to replenish the electrolytes in your system. If your condition is not getting any better after 2-3 days, consider seeing your GP for an assessment.
-Dr Quan