Does the stomach flu make sick on and off different days? eg normal one day sick the next

That can happen: The intestines don't digest or absorb food and drink properly during a "stomach flu" infection. Some days are better than others, but symptoms often depend on what one eats or drinks, and especially on the quantity eaten or drunk. That means what comes out as diarrhea often depends on what goes in the mouth. After the first 2 days, the general trend should be gradual improvement.