I can truly empathize, Liz. Hugs. I've cried many a time in the past with Killian. At one time he lost 15 lbs. in 2 weeks when liver disease was first diagnosed.
Braunschweiger sometimes works, salmon with oil, peanut butter, tuna, cheese....
Good luck on finding something. Which anti-biotic is he on? Sometimes that will give him a stomach ache.
My heart and prayers are with you and Smokey.