Do I have an STD; more importantly, HIV?

In December of 2010, I was taken advantage of by someone I considered a friend, and had unprotected vaginal intercourse. In February of 2011 I went to get tested for every STD. It all came back negative, and I was so relieved; but I cant stop thinking about it because I am extremely paranoid that I might have HIV, and because the test results stated underneath that even though it is negative, it may still be positive. I don't believe to have any symptoms, like getting Thrush or having swollen lymph nodes, and there is no uncomfortable sensation during urination, but I have a cough that is persistent, and I'm just so scared. I'm 23 and it has been six months since the incident, and four months since I got tested. I guess what I'm asking is, should I have a real reason to be worried about having HIV, and get tested for it again? I'm so sorry if this is a jumbled mess of thoughts. I would really appreciate any feedback. Thank you so much.�