Taraann, my son, who is ten, has a similar situation. He cultures staph, pseudomonas, stenotrophomonas and MRSA - also two funguses, aspergillus and something else(?).
He was having repeated hospitalizations and was on constant rotations of Zyvox and Cleocin , along with the Bactrim that he's on all the time.
In August the doc put us on six months of Sporonox (anti fungal) and Doxycycline, which is an older AB. He continues to take Bactrim and Zithromax (3x/week). This has made a HUGE difference! When he does get sick we go to Zyvox and Cipro for 2-3 weeks, sometimes with a burst of steriods. This gets him over the hump, then it's back to the Doxy.
So, I guess the point is, there ARE some other ABs out there that may work and maybe ask about treating the aspergillus/fungus issues directly-not only the symptoms, ie the steroids he's on.
There is also some research out there about using some anti TB drugs vs MRSA.
Don't get me started on how mad I am that no one even thought about eradication therapy when he first cultured pseudomonas OR MRSA.
Last thought is don't be too afraid of being on AB all the time. I was, but it has made such a difference in his and our quality of life.
Good luck with this very frustrating situation.