Hi, Miasmomma, a lot of the people you are posting to and asking about their test results have not been in this community for years.
Your explanation doesn't throw any doubt on the pregnancy tests, the doctor, or the DNA lab, who sound like they were all performing their jobs professionally. Even if you ruled out one or two resources, you would still have the data from the other(s). It sounds like all the medical evidence gives a consistent answer.
Given that you have the answer but are still freaked out, see a counselor, pastor or therapist. Identify what the anxiety is really about, and work on addressing that, and your obsessive desire for reassurance about paternity will fade away. If you're going to devote the time to worrying, put it into solving the real issue(s) that you face, not this false concern about paternity.