Sounds like you got a false positive on the first test. It's unfortunate, but it can and does happen with any test for any disease.
If both of your partners tested negative, they don't have HIV and couldn't give you HIV. If you had had HIV for years (prior to those two relationships), all of your tests would have been positive.
What kind of test were the 4 most recent tests? RNA, antibody, or Ag/Ab?
What was your risk? Oral anal or vaginal and did you use a condom?