C.W.
Hi luv-
This is gonna seem a bit off base...
BUT
One of my kiddos had some HUGE medical issues...but one thing that kept happening was low grade fevers for seemingly NO reason...
We finally figured out she was 'micro' aspirating...inhaling enough to kind of 'piss off' her lungs...but not enough for anything to 'show' on ex ray or bloodwork...
Just a thought.
Best luck!
michele/cat