As someone who used to work a sex info hotline in San Francisco, I have to say that HIV tests can now detect HIV antibodies in the blood (the sign that you have the AIDS virus) as soon as two to four weeks after the sexual encounter.
They do test donated blood for the HIV virus, so if you were invited to donate again, you can rule out HIV infection, HOWEVER that is not how you should be managing your sexual health. Diseases like herpes and HPV (warts) will not show up in a blood test at a blood bank. And those you will have for life.
Michelle is not accurate in her statement that if you have sex with a person who is HIV+ that you will have to continue to be tested for sero-conversion for the rest of your life. If you do have unsafe sex with someone who is HIV+, or who contacts you to inform you that they have learned that they are, you do need to get tested, but testing at one month or later does give an accurate exposure answer. You can't sero-convert years after a single exposure.
Essentially, since the blood bank didn't call you and tell you that they found a blood-born STD in your blood sample, you can rule out having any of those, however, that doesn't mean you didn't get one of the other ones. Herpes, warts and chlymidia all wouldn't show up to them.
If you need more info about safer sex and how to protect yourself, or you need to find a clinic for testing, you can visit
http://www.sfsi.org where they have tons of info, and you can call or email them with specific questions.