Welcome to the forum. Thanks for your question.
The HIV blood tests are among the most accurate diagnostic tests ever developed, for any medical condition. If done sufficiently long after the last possible exposure, the results are 100% reliable and overrule all other considerations. In other words, even after the highest risk exposures, or in the face of typical symptoms of HIV or ARS, the test results rule.
And your tests are 100% reliable. The results you had by 42 days were conclusive; all tests after that were superfluous and unnecessary. Your symptoms are not typical for ARS, but it wouldn't matter if they were. To your specific questions:
1) With those results, there is no possibilty you have HIV.
3) With the modern tests in regular use, "late seroconversion" is an urban myth. It doesn't happen. Also, the term "seroconversion" is pertinent only to the antibody tests; you had PCR and p24 antigen tests as well.
4) Actually even earlier: 4 weeks is definitive for the combo test. Even for the stand-alone antibody tests, 6-8 weeks (not 3 months) usually is conclusive. Below are a couple of threads that discuss HIV test timing, including an explanation why 3 months remains official even though test results are reliable at 4-8 weeks.
So all is well, no worries. Don't have any more HIV tests!
Best wishes-- HHH, MD