Hey Tara,
Your post described my own symptoms almost perfectly, so I know exactly what you're going through. The worst part is the sense of being constantly on the brink of infection - that inevitable combo of tiredness and coughing that starts up within weeks of finishing the IVs. Believe me, I've been there and I totally admire you for pushing through it, having the courage to keep your head up, and working to try and find a solution. I don't think CFers get enough credit sometimes for how hard we work just to manage this disease and keep on living life. So my first comment is: good work and go you!
That said, after having a year of ups and downs with PA (during which I was tested for all the normal allergies and other things people have already suggested), my doctor and I finally agreed to an extended course of prednisone - 30 days (40 mg for 5 days, 30 for 5 days, 20mg for 10 and 10 mg for 10). It's not an easy drug to handle, and it's for inflammation, so it doesn't "treat" the PA infection per se, but it has really been a life changer for me. Apparently the constant infections were causing my lungs to be inflamed all the time, and that lead to more and more infection in a sort of circular roller coaster. As soon as I got on the prednisone my cough started to stabalize, my weight came back up after a year of being down due to ravaging infections, and my energy began returning since I could finally breathe deeper. With the increased weight I am much stronger and better able to fight infections, and the prednisone gave my lungs the "break" they needed to regain some stability. I started exercising again, and the future looks much brighter overall. My lung function didn't really improve too much, because like I said the prednisone won't treat the bacteria, but it certainly did get infections under control. While not quite the miracle treatment that we're all searching for, it really did make a noticable difference both in my pysical health and my mental outlook. There is something to be said for just going a couple of months without a flare up...it makes the whole thing easier to face.
The other plus side: if you're like me and have difficulty maintaining your weight, the prednisone has the added boost of giving your appetite a jump start. I have gained a MUCH needed 10 pounds since November (thank you, Ensure Plus). I also tolerated the drug remarkably well, although I did experience difficulty sleeping. Definitely have a frank discussion with your doc about the side effects though, particularly if you have low bone density or are worried about CFRD.
Good luck fighting this thing. You sound like such a strong individual, just like so many others on this forum who inspire me with their stories.