So sorry to hear this. I've actually heard from various docs that once you send out for synergy testing, there are many effective combos that often come back... You just have to know which to use to treat. Even if you're resistant to one med on its own, it may very well work in combo with another one or two meds. It usually (or so I've heard) takes a VERY long time before even combos of meds will do the trick. So, that's something to keep in mind. It just takes longer to send off the culture for synergy testing, etc.
Best of luck to you and your little boy.
P.S.... I agree that writing a letter to the FDA explaining your situation would be extremely beneficial at this point. I've heard amazing things about Azli, but since the FDA denied its release, we are stuck with limited options with regard to inhaled/oral meds. 2 inhaled abx (which many people are resistant or can't tolerate) and one oral abx. to treat PA is measley and pathetic.