I had much the same situation with Redemption, my very first guinea pig (over there in the avatar). I was fortunate to find a diggable spot in the woods to bury him. It's just sometimes no matter what you do they just won't get better and keeping them hanging on would make it worse, and we don't want to do that. I know the empty feeling; I never thought I would ever miss a guinea pig, but I do. Here's hoping things ease for you very soon.