I think a change in diet could be something you could try, if you haven't already. I was skeptical that food really could make a difference, but with Onyx's ever-so-frequent bladder infections this year I finally thought I'd give it a shot. We added more litterboxes in more available places for her at the same time, so it's hard to know for sure whether that or the change in food was what made the difference, but there has been a huge, huge improvement in Onyx so I'm hopeful the food might be part of it. At any rate, I'm sorry to hear Luna is sick again, that's hard, and I'll keep my fingers crossed that things get better soon !!!