Since HIV tests actually test for the presence of certain antibodies produced specifically to fight HIV, the test should take place approximately three months after the possible exposure. Another test after six months is also recommended, as it rarely takes longer than six months for the antibodies to be present.
http://www.homehivtestkit.com/hiv-symptoms.html (http://)


Activities such as unprotected heterosexual or homosexual sex or needle sharing can put a person at risk of contracting HIV. If you engaged in such behaviors or if you feel you are at risk for any reason of having HIV, the best thing to do is to get tested immediately.
b If the HIV tests are negative, you should re-test yourself again after three months as the infection can take longer to show up in some people.