What medicine i need to take for gastro ?

Depends on severity: Normal healthy people can get stomach flu or food poisoning symptoms occasionally. One will usually vomit until her stomach is empty, which is why it is important NOT eat or drink anything for a few hours afterwards. Then a usual treatment is small amounts of Pedialyte or broth, maybe 1 ounce every half hour while awake. If worrisome symptoms, very young, very old, or very frail, doctor can check.