Hi Michelle,
 
I don't know how thoroughly your vet checked your little guy out but if
the only thing wrong with him appears to be a low weight and testiness it
hardly seems to be a reason to put him down.  Is he eating at all?  Is he
pooping?  I would try him on a round of Amoxyl drops.  My "little" male
(only two pounds top weight ever!) has twice gone through something like
you are describing, each time about a year apart.  After the Amoxyl he
perked right up and increased his eating.  The vet thought it was possibly
an intestinal bacterial infection such as heliobachter which can cause
small ulcers to the digestive system.  Whatever it was - it made a huge
difference in his eating and he picked back up the 3-4 oz.  he had lost
each time.  Also since he is a rescue you might try giving him a mixture
of foods and watching closely to see WHAT he eats - perhaps he has only
one favorite and isn't getting enough of it.  You might also look at his
teeth - pain from a broken or infected tooth might cause the symptoms he
is experience too.
 
I wish you much luck with your fuzzle - don't give up on him now!
 
Karla
Meep and Daisy
[Posted in FML issue 2785]