An upset stomach can be a result of many things. When symptoms include vomiting, diarrhea, and fever, chances are it's a viral infection.

"A viral gastroenteritis, which we sometimes call 'a stomach bug' or 'a stomach flu,' is a common reason for having an acute onset of vomiting and diarrhea, and sometimes with fever," says Dr. Tina Ardon, a Mayo Clinic family medicine physician. The viral infection is mostly commonly spread through contact with an infected person or by ingesting contaminated food or water.

Watch: Dr. Tina Ardon explains viral gastroenteritis.

Ensuring you stay hydrated is imperative. Dr. Ardon says a person can become dehydrated quickly, even with a couple hours of vomiting or diarrhea. "When we say dehydrated, we're usually referring to a significant amount of fluid loss—either from vomiting or diarrhea."

It's important to stay hydrated with fluids, but what about eating?

"Most patients have heard of something called the 'BRAT diet,' which stands for bananas, rice, applesauce, toast—basically indicating blander foods, softer foods that are gentler on the stomach," says Dr. Ardon. "However, studies actually show that if you're starting to feel better, resuming a normal diet is very appropriate. So one can consider that vs restricting their diet if they're otherwise feeling better."

Most cases of viral gastroenteritis will last about a day or two, and will resolve on their own. "If things are continuing to improve, it's probably safe to continue watching for a couple days, but after that, if you're not having resolution of your symptoms, that's a good reason to go see your doctor," says Dr. Ardon.