I had an endoscopy which found gastritis in the stomach antrum. i have been feeling nauseous quite often. is this from the gastritis or functional?

Hard to know...: Perhaps the answer will become apparent after you show response (or not) to treatment of gastritis, or if you identify situational triggers to symptoms.

Gastritis: Very likely associated with gastritis. Recommend antacid medication, if symptoms persist, i wold get an abdominal ultrasound. Make sure you were also tested for h pylori infection.