I might as well add in (since people have already got the husbandry needs down) that the snake's body is getting immune to the injections so the injections MAY not be working as successfully as it did the first time. It's the same thing when you take medicine too much, like when your sick and take some Robitussen (sp?) or Tylenol too much. Each time you take it your body starts to become immune to the effects of the medicine so once you've taken it too much (not from only ONE time your sick, but maybe a few other times) you can't use it anymore because your body has become immune to it.
Sorry if that was a little confusing to explain.