Is it possible that Baytril injection could have killed my dog?

[Kodak2017]

Told the vet my dog had diarrhea, lack of normal appetite, and moving around slower.  The vet didn't even examine him at all.  I asked if my dog could have intestinal obstruction.  He said "no." And that if that were the case, my dog would obviously be in pain.  Vet just simply gave him an injection of Baytril-Dex-B12, and Ketofen.  Two days later he died.   I remember in hindsight that I forgot to mention that my dog also seemed to be constipated - besides occasional diarrhea, he seemed to force when squatting to poo. And so on that same night of the vet visit on 9/18/2017, he ate well, but then threw up all his food, undigested, an hour or so later. The next day he did not want to eat at all, and started throwing up brownish bile. I also noticed in the morning, his eyes had dried eye discharge on the inner corners of his eyes. I feel so angry and devastated.  I counted on vet to recommend best course of action.  You know, first thing first.  He only mention bloodwork casually, as if it was secondary to giving my dog Baytril, etc. injection and Ketofen first, before even performing a thorough diagnoses of my dog's condition/health.  All he checked was my dog's temperature, and it was normal. No de-wormer, because he was clear of intestinal parasites.  He was 11 1/2 years old, and truly, the most loving, affectionate,  and best dog ever.  He deserved better.  I really need help understanding what happened?  Now I am suffering from GUILT AND DEPRESSION.  I feel like I let my dog down.  I know in my heart and soul he could have lived longer.  As of 8/20/2017 I noticed he started feeling like not all was well, I thought it might just  be some isolated incident that would pass with little time.   He passed way on 9/20/2017.  I did notice some blood and mucous in his stool sometimes.