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Testing for HIV 5 days after the exposure will not be of much use except to know about the previous exposure status. Nausea
are not usually early manifestations of HIV. Earliest manifestations due to HIV is unusual to occur earlier than 4 weeks after exposure. So your problem may unlikely to be due to HIV.
But unprotected sex may likely to be risk for other STDs including Hepatitis. If there was oro-anal contact , there is likely possibility of nausea and diarrhea. Loss of appetite is likely to be due to Hepatitis.
So repeat the test for HIV with P24 antigen or a PCR or a Combo test after 4 weeks along with tests for other STDs like Hepatitis B
and C, Syphilis
and also for Gonorrhea
and Chlamydia to assure that you are free from STD/HIV.
Your present problem of diarrhea may be due to oro anal contact or not related to STD.
Consult your physician and get well soon.