If your first died within the first week and your husbandry was at least close to right, I don't think you bought a healthy snake to begin with. My friend had a similar experience. She had hers for two weeks. She had brought it to the vet about a week before it died, and had another appointment to liquid-feed her snake. When it died the vet told her that it wasn't her fault and she had literally done everything possible to save the snake.
It sounds like you really care for your snake! I was a little bit paranoid when I got my Jackson, so I actually took him to the vet for a preliminary health checkup. I know some would call that overkill, especially those who have hundreds of snakes to look after, but it gave me some peace of mind!