Bethy - you may want to consider alternating TOBI with colistin, I recently switched off of TOBI to colistin and was having much better results now I am trying cayston. I dont have plans to regularly alternate but if I did it wout by colistin.
Day 3 of cayston here, too early to say anything, I am in a sense giving myself a 'mini' tune up since I went directly from colistin to cayston witout an 'off' month which I normally would have. So, that being said, I would expect to be doing well/feeling great and not getting much up. I had a large amount dark green I have gotten up already which is abnormal for me. Too early to tell anythign for sure but its looking good.
Now I just need to get the washing down and not have my counter look like a dishwashign factory--pasta pot for the regulare nebs, dishes water and alcohol for altera, baby bottle rack, towels, sterilizer, its a bit much.