I Am 68, Male And Have Been Diagnosed On Monday

I am 68, male and have been diagnosed on Monday with the flu. I have a low grade fever, achy, headache, tired, lack of appetite, bad taste in my mouth and generally not feeling well. When diagnosed, I was not given any tests to determine it was the flu. One week earlier, I went to an ENT and was told I had a sinus infection and was given antibiotics for 10 days. Since I was not feeling any better, but worse, I went again, but to a different doctor this past Monday. They told my I was probably on the downside of the flu.
Can something else be going on?