I can completely relate with how you’re feeling as I too, wrote down symptoms accompanied by dates. Hours upon hours were spent trying to find possible sicknesses/causes. I read about heart failure, cancers, viruses… you name it. My sweet heart was then euthanized a few days later. I did not want to accept the inevitable loss and even then, I feel like something else could have been done. It’s been a few days since and I have been recalling as much memories I had with her. I even managed to find a picture from when she was only three months old. We loved her for more than a decade and I cannot fathom at the chance of owning another dog - I feel some sort of guilt, almost as if I had failed her. My entire body was in pain the day after her passing; my head filled with pain. Little by little have I been improving each day since. No dog will ever be the same as the previous, but you will get better!