Hello from JustAnswer.
It is vastly most likely that this is a viral infection of the gut. Although commonly called a stomach flu, the more proper term is a viral gastroenteritis. If neither the exam, blood tests, or the CT scan indicate another cause, it is appropriate to manage this as a viral infection. So, there is no reason to seek another opinion regarding the diagnosis.
However, the other issue when dealing with a viral gastroenteritis is whether fluid status can be maintained. The human body can actually go for a much longer period of time without food than it can go without fluids. If a severe gastroenteritis is preventing adequate fluid intake, then a person may become dehydrated long before 2 weeks have passed. Consequently, it would be appropriate to be seen sooner than 2 weeks if dehydration is suspected. There are several things that can be monitored at home to assess whether you may be getting dehydrated. The simplest is to monitor weight on a daily basis. This works better if the weight immediately bofore getting sick is known, and then any rapid weight loss during the illness is typically due to the weight of the water that is lost. If the weight immediately before getting sick is not known, then the weight obtained earliest in the course of illness would be the point of reference. A 5% decrease in weight is getting significant, and you should significantly increase fluid intake, but a 10% decrease is a sign of more severe dehydration and you should be seen, even if it has not yet been 2 weeks. Symptom of lightheadedness, rapid heart rate, or a significant decrease in urine output also may indicate that dehydration is starting.
If you can get adequate fluid intake to stave off dehydration, then it would be OK to wait to see if the symptoms improve spontaneously. The vast majority will improve with supportive care, but it would be appropriate to be seen again if the symptoms have not improved by 2 weeks.
Intake of food/calories can wait until there is no longer any fear of inadequate fluid intake or dehydration.
If I can provide any clarification, please let me know.