No, you don't have the flu already. It's probably COVID.

• If you have a headache, fever or sniffles it's likely COVID-19, not an early bout of the flu.
• It's rare to get the flu in the late summer and early fall, an expert told Insider, but COVID-19 is still around.

Feeling feverish? Got a cough or a headache? You probably don't have an extremely early flu, but actually COVID-19.

"We know that flu really is seasonal," Dr. Noha Aboelata, an Oakland, CA-based family medicine physician told Insider. "We can even look at wastewater and see that while COVID is certainly still circulating in the environment, there actually isn't a flu A or B circulating at the moment."

COVID-19 is rising, according to wastewater data

When people get COVID-19 or the flu, some of that virus gets flushed down the toilet when people use the bathroom. These viral particles can then be monitored via wastewater sampling.

Monitoring wastewater gives researchers a pretty good idea of whether COVID-19 or the flu is circulating in a community.

Right now, the coronavirus is still being detected across nearly all of the testing sites in the United States sampled by Sanford and Emory University-backed initiative WastewaterSCAN. Samples of the virus have been gradually on the rise since the beginning of the summer, potentially thanks to the new "Eris" coronavirus variant, or potentially the even newer "Pirola" variant.

Data from the Centers for Disease Control and Prevention (CDC) also shows that hospitalizations from COVID-19 are up 19% in the past week, and deaths are up almost 18%.

On the other hand, the flu has been almost nonexistent across testing sites since the beginning of June.

The CDC also tracks flu cases throughout the year. The agency found that during the last week of August, less than one percent of samples tested were positive for the flu, down from a high of 26% last December.

Symptoms of COVID-19 can feel a lot like the flu

The flu and COVID-19 are both respiratory illnesses, and can lead to similar symptoms like a fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches and fatigue, according to the CDC.

But it's important to know which illness you actually have.

The progression of COVID-19 and the flu differ in key ways. First, those who contract COVID-19 are likely to be contagious for a longer period of time than those with the flu, making it easier for someone who is infected to spread the virus to someone else.

Additionally, people typically only catch the flu once every few years, but people can re-catch COVID-19 more frequently. "We definitely have heard of people getting it multiple times per year," Aboelata said.

The CDC says that overall, COVID-19 causes more severe illness in some people and has the potential for long-term complications, although both viruses can result in severe illness.

"We are seeing some evidence that there is cumulative nature around some of the harms of COVID," Aboelata said, "so we know that each time you get COVID, of course, it's a new opportunity for a bad outcome."

Mistakenly thinking you have the flu could lead you to delay timely treatment, or accidentally expose other people to COVID-19 if you aren't isolating.

"I think the most important thing is that you actually don't know what it is unless you get tested," Aboelata said.

There are also other reasons for why you might be feeling under the weather

If you don't have COVID-19 or the flu, you may still be dealing with another condition that causes similar symptoms.

Allergies and the common cold can both occur year-round and cause runny noses and scratchy throats.