The pain we feel from the death of a pet is the blood price we pay for the joy they bring in life.
It is always too soon, and there's always regrets. Not sure if you've lost a family or close friend yet, but it's similar for humans. It's harder for pets in some ways because, as you're feeling now, there are things we might miss due to the lack of communication.
You may blame yourself forever, but you shouldn't. Instead, it's a lesson in care for a future pet. I've learned over the years to be very aware of things and be overly cautious with taking them to the vet, and I also am an advocate for pet insurance. I'm lucky to have the means now that I don't have to worry about vet bills, but it wasn't always that way.
My pets now get the best care and the best quality of life because I want them to have a better life than how some of my pets lived when I was younger. I've learned, and I hate myself for how I was, but all I can do is learn and be better now. My pets deserve it.
If you felt like you gave your dog had a good life two week ago, then that's all that matters, not that you didn't recognize the symptoms.
I'm so sorry for your loss. It's an awful thing, and I can't imagine the guilt you're feeling even if I don't personally think you should be feeling guilty, for what it's worth. Those feelings are normal, know that. It's part of the grief. It's part of the price we pay.
When my pets die I will feel the same things again just like you are now, but it won't be my fault then even though I will feel it, it's death. It's the other side of the coin of life - all things die, it's part of the process.
Good luck stranger