Oliver's Struggling Again

Following the two injections a week ago Oliver was so well, but we are now sadly back to square one. He just will not eat. Last night Steve gave him another B12 injection, but this morning though he's quite bright he still will not eat. I posted on Facebook and had a few suggestions of things to try, like homemade honey and chicken soup. I made it, he won't eat it! This morning he ate a couple of licks of warmed pilchard in tomato sauce .. but no, nothing else. I'm now waiting for the vet to get back to me as I rang to ask if he could maybe have some palatable steroids. I have some but will not give them to him without getting advice first.
A few people suggested I syringe some soup into him. For me that is a fine line, force feeding an old cat isn't really something I want to do. If he was a youngster recovering from an illness or surgery then of course I'd do it, but Oliver is not going to recover we are just trying to keep him comfortable and give him the best quality of life whilst he's still with us and still bright. Today Oliver is not ready to leave us ... tomorrow or the next day may well be a different story.
I wonder why old cats do it? Why do old cats just stop eating? I know kidney failure is so common in old cats .. maybe there's a correlation?
I'm on pins now waiting to hear from the vet, I considered taking him for blood tests, but really what for? I know the answers and I don't want to put him through the stress at this late stage in his life. The hardest part of loving is knowing when to let go, and Belinda's words are always in the forefront of my mind, better a week to early than a day too late!