You will always get a negative test result. The results can't change since oral is not a risk for hiv.
Your doctor is speaking about 'theoretical' risk which is different than real risk. In all these years of HIV being a thing, no one has ever gotten HIV from oral sex. Not a single proven or documented case ever. I would not be worried about this event. ALL tests (hiv test, regardless of type or generation) done at 12 weeks or beyond are accurate.