HIV is merely your anxiety obsession. From what I've seen, most anxiety/panic disorder sufferers have a particular worry in mind, and I guess this kind of obsessions stem from the similar parts of the brain that causes OCD (which is also categorized as an anxiety disorder)
For me, I was scared of schizophrenia. Everyday I would check for symptoms and reassure myself temporarily, only to be scared again (this is inevitably if I keep up with this mentality). I would check for voices, self-diagnose with schizophrenic symptoms, ask my doctor, etc, and in retrospect I found this really silly. What I, and you, need to wrap your mind around is that it is your ANXIETY playing games with your mind. In turn, your fear perpetuates this anxiety. Not even knowing you, I am willing to bet $1000 dollars that you are not HIV positive. I can assure you it's merely the object of obsession for your anxiety. This is obvious by the fact that you can never seem to be assured; when you get your negative results you start to doubt that you've been given the wrong report, and who knows, when that has been assured you find some other reason to be anxious about. My advice to you is to keep telling yourself it is merely your anxiety playing games with your mind. I know it's hard but I can assure you that is what is happening. Once I realized this I have become much much better. Cheers.