Poor Couver and you.
I am very sorry to hear he is sick.
I agree with Vicki, has pancreatitis been ruled out? Is it the cPL blood test?
Also, does Couver normally do well with pumpkin? For my Teddy, tt makes diarrhea worse. I would try leaving it out. Just feed chicken and rice and see if that helps firm things up.
Sending positive thoughts for your little boy.