Started with sinus infection now have respiratory infection and body aches from head to legs. Flu or pneumonia?

Maybe It's Flumonia. Good question. And could be both. But if, as you say, it started just in the sinuses and then spread, it's less likely classic flu. And if it spread somehow into your lungs and caused an infection then you'd probably feel pretty bad, so I'd suggest you get examined by a doctor, who will decide what, if any, test(s) he'd decide to get. So, it sounds like it's time to be seen in person!
Could be. Either or even both. If you are worried, seek an in-person evaluation with your primary care or at an urgent care center.
Either or both. start, and symptoms overlap! Get the flu followed by respiratory secondary infection has been common this season.

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