Is it possible for anxiety to cause stomach/gastrointestinal issues?

I've had on and off stomach issues for the past 3-4 years and ive noticed they only seem to show up during stressful parts of my life (stress in school, exams, travelling, financial issues, family issues, etc).

Ive gone through multiple blood tests, upper GI series (barium xray), and ultrasound but all tests came back negative. My symptoms always mimic that of an ulcer (constant hunger followed by no appetite, vomitting at night, diarrhea in the morning, burning stomach, etc).

I finally went to a GI specialist who said i have non-ulcer functioning dyspepsia (discomfort if i eat after being hungry for a while) and possibly gastroparesis (stomach not digesting fast enough).

Do you think this could all be caused by anxiety since the tests never came back positive? How should I handle this? It's starting to affect my life.