I still go through bouts of nausea, even at 33 weeks. Sometimes, I'll go a week or more without anything, and then all of the sudden, it'll hit me one day and I don't know if it's pregnancy related, or, like your concern, the stomach flu. So far, I haven't had the stomach flu though.
Just make sure to stay hydrated, rest when you can and if it persists into tomorrow, maybe it's the stomach flu. Either way, no one can do much about that, unfortunately.