The flu going around here (that did not make it into the flu shot this year) has some very nasty secondary stuff that I am still recovering from, including pericarditis. I did not ger pneumonia this time but I know of a ton of people that did, as well as reactive airways even in people who usually don't get that.
So definitely worth getting checked out if you are still very ill weeks later, or if you get better for a little while and then get hit with fever again. I know a lot of people who got strep immediately afterwards too, often with atypical symptoms. I know it's a big expensive deal to go to the doctor but honestly this season's illness i would.