Feeling waves of nausea that comes and goes today. Stomach flu? Something else?

Stomach Flu. Gastroenteritis symptoms may include: diarrhea, nausea, vomiting, abdominal cramps/pain, headaches, muscular aches ; pains as well as fever (low grade). Bloody stools are not usually associated with gastroenteritis.
Not enough info. So many things can cause this that it is impossible to guess - if it persists a person with this symptom should see a doctor.