Gary brings up good points about your immune system and WBC. My WBC just got into normal but still low and I just got over a dussy of a sinus infection that I never remember having so bad. I was a little freeked about if it was something else in the sinuses when I had it. Mine was curred after two different types of antibiotics. Some times you need different ones to do it. Also the yellow stuff is a good sign that it appears to be infected not something else. Keep on telling your regular doctor and time or other antibiotics should do it.