The information provided by the nurse is insufficient and
possibly inaccurate, unless the staph
was "coagulase negative". Even if it were, the presence of pus cannot be ignored. The pus could be caused by what are called Anerobic Bacteria, or Fungi. Yes, the Augmentin, considered to be good therapy for acute sinusitis, could give a misleading culture.
If you are not feeling better, even a little, you may need an alternative antibiotic.