New diagnoses like these can be very scary, especially when we resort to Dr. Google to learn more. You will find this community on Mayo Connect to be very helpful, as we are patients who have been through what you are dealing with. I wonder if @betsey can share her experience, and what finally worked for her.

If your ENT did cultures, there was also probably a sensitivity test done, which showed them that Clindamycin and Gentamycin are effective on your particular strain of pseudomonas. If you do not improve in a month - yes, it takes at least that long for sinuses - they may opt for different drugs. The rule of thumb is to start with the safest medication likely to be effective and move on to the "bigger guns" is needed. If you do not feel your doc is familiar enough with this, you could ask for a consult with an Infectious Disease doctor as well.

How did you get Pseudomonas? It's everywhere, and usually just gets trapped in your nose where it doesn't cause an infection. But, if you have and autoimmune disease or get a virus or other infection that knocks down your body's immune defenses, it can colonize and cause a symptomatic infection. If you get a cold, and blow your nose too vigorously to remove thick mucus, you can force the germs up into your sinuses, where they grow in the nice, dark, warm moist environment.

Have you started the antibiotics, and are you feeling any better?

PS I have had pseudomonas in my lungs, but not my sinuses.