You NEVER had an HIV risk, so while you are choosing to test, you don't need to. When you do test, believe your results. Do not "what if" yourself into thinking the test results couldn't possibly be accurate. You have taken basic statistics about the functionality and accuracy of the tests and turned that into reasons to not trust your results. That's 100% anxiety talking.
Based on your above response, I can tell you you are spending WAY too much time "reasearching" this. You are effectively fueling your anxiety by doing so.
The very best thing you could do is the SHUT OFF your computer and don't spend another second reading or searching about HIV, HCV, testing, or anything else that is related, and seek some professional help. You are "what iffing" yourself into a frenzy....sadly, over a no risk situation to begin with. YOU DO NOT HAVE HIV.
Take a simple antibody test and accept the results...after a year and a half, there is simply NO way that you could be positive and have a negative HIV result. It's impossible. You are taking information from the internet and twisting it to conform to your anxious deductions. If this was as realistic of an issue as you have made it (delayed seroconversion and inaccurate testing)...there would be all kinds of people reporting issues, and there simply isn't. HIV testing couldn't be more straightforward. The rationale behind the testing is so simple...if you're infected, the test detects the antibodies that your body will produce...if you're not, they won't be there and nothing will be detected. It's really as simple as that. Honestly, you'd be smarter to worry about being hit by a meteor, at the same time you win the powerball.
Again, remember, from what you've said, you would have never been exposed to HIV to begin with. Please get yourself some help. There's nothing more we can add. Feel free to report your negative result on this thread when you get it, but otherwise, there is just nothing more we can say. This is a very busy forum and we try to get to everyone's questions as quickly as we can, which is why we cannot spend an endless amount of time repeating ourselves to reassure people. Consider yourself reassured.
You can always pay the fee and post in the expert forum, where one of the doctors who have specialized in treating HIV for decades can offer you more reassurance:
http://www.medhelp.org/forums/HIV---Prevention/show/117
Maybe an explanation from one of them will finally put your mind at ease, although from reading your posts, I suspect that your anxiety really has its hooks into you...which is why you really should seek some help.
Good luck.