Welcome to the forum. Your questions are among the most common asked on this forum, so my replies are brief. Below are some other threads that provide more detail.
The bottom line is that you for sure did not catch HIV and should stop testing. HIV test results always overrule symptoms and exposure history in judging the possibility someone is infected, and your results prove you do not have it. In any case, you describe a low risk exposure and your symptoms are not suggestive of a new HIV infection anyway.
You misunderstand the essential elements of HIV test timing following exposure. The common advice for 3 month testing applies only to the stand-alone antibody tests. Even that is too conservative; such tests almost always are positive by 6-8 weeks. However, you had the duo test -- which is 100% reliable by 4 qweeks. Your last 3 tests were superfluous; you could have been certain 2 months ago that you didn't catch HIV.
If your symptoms continue and/or you remain concerned, see your GP or other health care provider about them. But stop worrying about HIV. For sure you don't have it.
Here are some other threads about timing of the various kinds of HIV tests.
http://www.medhelp.org/posts/HIV-Prevention/Confused-over-testing/show/719310
http://www.medhelp.org/posts/HIV-Prevention/-A-Question-on-Testing/show/1347755
http://www.medhelp.org/posts/HIV-Prevention/Need-your-help/show/1345664
Regards-- HHH, MD