I have done test on hiv after 3 month, using the 3rd generation rapid test, and the result is negatif, but why i have symptom before the test?

Test is conclusive: HIV test results always overrule symptoms, if the test is done sufficiently long after the last possible exposure -- and 3 months is plenty. The symptoms of HIV also occur in a hundred or more other medical conditions, most of them a lot more common than HIV. Your test result proves that HIV is not the cause of your symptoms, no matter how typical of HIV they seem to be.