While we're in the midst of the most severe flu season of the past 15 years, the U.S. is also seeing increased rates of norovirus.

The situation with both illnesses isn't great right now, Dr. Richard Martinello, infectious diseases expert and Chief Medical Officer for Yale Medicine, tells TODAY.com.

"It's not unusual for norovirus to have bad seasons every two to three years, and it seems like we're having a worse than typical year this year," he says. And, with flu, "we are having an exceptionally bad year."

Not only are a lot of people getting sick, but there are also more people than usual developing severe flu symptoms, Martinello says. "In our hospital area, we have about two to three times as many people as we would normally see hospitalized with flu," he adds.

This year's flu season has also been so severe that some schools have had to close temporarily.

"It's a pretty intense season," agrees Dr. Stuart Ray, professor of medicine and oncology at Johns Hopkins University School of Medicine.

And, knowing that there's likely overlap in where these illnesses are spreading, "there could be confusion" between norovirus and flu symptoms, he tells TODAY.com. Adding to that confusion is the fact that some people might refer to norovirus as the "stomach flu," which isn't a correct term, the experts say.

A mild norovirus infection might just cause some loose stools and loss of appetite, Martinello says. But a more severe bout can come with a fever. And, with severe vomiting and diarrhea, dehydration is also often a worry.

Unlike norovirus, influenza typically causes respiratory symptoms and a fever as well as a headache, body aches and general feeling of malaise, Ray says.

Here are the typical symptoms of the flu:

Some people will also get gastrointestinal symptoms with the flu, but that is rare, the experts say.

Among kids, as many as 25% of those with influenza will experience vomiting or nausea, Martinello says. "So it has some degree of frequency. But in adults, it's actually pretty uncommon," he explains.

It's important to know which of these illnesses you have because there are vaccines and treatments available for the flu. Although we don't have those tools for norovirus, there are other helpful measures you can take to prevent the virus from spreading.

When looking at the lists above, you'll see some overlap between norovirus and flu symptoms. But the two illnesses tend to manifest pretty differently, the experts say.

While both can cause gastrointestinal symptoms, for instance, those signs are the main feature of norovirus and only occasionally show up with flu infections. Those symptoms also tend to be more intense with norovirus.

For instance, with norovirus, "the diarrhea is typically pretty frequent and very watery," Martinello says. And, when they've been vomiting, people with norovirus may have a hard time keeping even water down.

But people with norovirus won't get the respiratory symptoms that are characteristic of the flu, like the congestion and cough, Ray says. The headache, sore throat and cough are symptoms that "differentiate norovirus from influenza," Martinello agrees.

And, although you can get a fever with norovirus, an influenza-related fever is typically a higher fever, Martinello says. "There can be fever in particularly susceptible people with norovirus," Ray explains. "But most people with healthy immune systems won't develop fever with norovirus."

Similarly, while the dehydration associated with a norovirus infection can make you feel achy, Ray says, body aches are a more classic symptom of flu.

When trying to puzzle out which illness you might have, both experts encourage you to consider the full combination of symptoms you're experiencing.

Ray also recommends thinking about which illness you may have been exposed to recently. If you know flu has been spreading in your office or that your child might have been exposed to norovirus at school, that can help you figure out which one you might have now.

Flu infections can lead to complications, such as pneumonia, Ray says, so it's important to keep tabs on your symptoms and get medical attention when needed -- especially when fever temperatures spike.

You may hear people refer to the stomach flu colloquially, but it's not an actual medical condition.

When people use that term, they might be referring to norovirus or something like food poisoning -- neither of which is related to influenza. That's why the experts that TODAY.com spoke to try not to use that term, and they encourage others to be more specific when talking about illnesses like these.

"When even physicians use imprecise language like 'stomach flu,' it gives mixed messages to people," Martinello says. And Ray agrees: When we use the word "flu" to refer to both influenza and stomach flu, "we're really making it tough," he says.

When doctors and the general public are more accurate with the terms they use, the experts say, that makes it easier to get you the right treatment more quickly.