Welcome to the forum and thanks for your question. It should have been in the HIV forum, but the "Important" disclaimer message about this is obscure and easy to miss. We'll move this to the correct forum.
Just yesterday I wrote a very detailed reply to a question about HIV window times. It answers just about all your questions about the HIV test results:
HIV symptoms are very nonspecific -- i.e. the identical symptoms occur in hundreds of other conditions, most of them far more common than HIV. In any case, your symptoms don't really suggest HIV anyway. They aren't typical at all, especially for an HIV infection that might have been present for several years. Therefore, test results always overrule symptoms. Your results prove you don't have HIV. Your symptoms also do not suggest any other STD. To your specific questions:
1-5) The answer is no to all. None of these scenarios is a realistic possibility.
6,7) No. Syphilis tests are highly reliable, and your symptoms don't suggest syphilis any more than HIV.
8) Yes, I would discount any and all STDs as explanations for your symptoms. In addition to the negative tests and the wrong symptoms, some STDs (e.g., chlamydia, gonorrhea) clear up on their own, without treatment, within a few months.
9) Xenotropic murine leukemia virus-related virus (XMRV) is a recently discovered virus once believed to be related to prostate cancer and chronic fatigue syndrome. More recent research has proved otherwise. As far as I know, its transmission has not been worked out. It is not considered an STD. There's a good Wikipedia article on XMRV.
For sure you don't have HIV or any other STD. You'll have to look elsewhere for causes of your symptoms. I doubt they have anything to do with your past sexual exposures. Most of them sound like pretty normal body sensations experienced by everyone from time to time.
I hope this has helped. Best wishes-- HHH, MD