It is unlikely that your current flu-like illness is related to your recent unprotected sexual encounter.  Most women do not have STIs or HIV and most single exposures do not lead to infection.  When they do, it is typically infections that cause penile discharge not flu-like illnesses.  

There are several STIs which can cause flu-like illnesses.  Hepatitis B can cause flu-like illness, as can recently acquired HIV.  If your symptoms were due to either of these STIs a test would be positive at this time.  It is far more likely that your symptoms are due to influenza, COVID 19, one of the every day, non-STI viral illnesses that we all get from time to time.  In careful scientific studies of persons at risk for HIV and STIs seeking evaluation, less than 1% of those persons have HIV.  The rest have the sort of much more common illness I mention above.

If you wish to prove that you do not have an STI, including HIV, test now.  If STIs including HIV were causing your illness the test would be positive.  I am confident that this is ot an STI.  EWH