A negative HIV test
after 3-6 month of risky exposure it self is more conclusive. There is no such things such as rarer strains. Autoimmune disease
false positivity is common not a false negativity. Extreme Late stages of disease there may be possibility described, Extreme late stage is obvious and will occur years after. The individual will be extremely ill and bedridden and counting his hours.
Most of the tests available are more than 98% sensitive and specific. For more confirmatory, two types of antibody tests with different type like ELISA
and a rapid or two different types of rapid tests are said to be confirmatory. So go for another test and with the negative result in your II test you are more confirmatory and reliable. Then you can forget the past.
practice is always good and alleviate unnecessary tension.