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Taking any form of medications prior to any testing for HIV, does not affect the test results in any way.
But, since it has been 28 days (4 weeks)and the window period is over , I would advice you to do the 4th generation HIV antibody (ELISA) test, instead of the HIV DNA PCR test.
Then once the test results are available, you should consult with your doctor for proper assessment and advice regarding retesting.
In case, you had a high risk exposure, you may have to repeat the same test (4th gen ELISA test) every 4 weeks , at least until 12 weeks for conclusive results.
In case, of low risk exposures, then your doctor may counsel you and let you know if the recent test is conclusive or not.
I hope this helps.