What do I do???

Question
Hello,

About a week and a half ago, I noticed my guinea pig was not eating, drinking or pooping.  I brought it to the veterinarian last Monday and was informed that its back teeth had grown over its tongue and that it had also developed an infection.  The vetirinarian gave me some antibiotics and filed down his teeth.  Well, it is now 11 days later and it is still not eating or drinking. The veterinarian said that its tongue was probably sore , but it looks fine to me.  I have been syringue feeding it mushed up pellets mixed with water, as well as mushed carrots and spinach.  I have also been feeding it some "TANG" orange juice for the Vitamin C.  Well, I am at a loss.  He is not getting any better.  He is resisting food more than ever, taking in less and less and looks awful (his eyes have little crystalized particles all around the eye, I am guessing from de-hydration since he won't drink).
All he does is huddle in the corner.

What should I do?  Am I just prolonging his misery and should I have him put down? I would really appreciate your input on this matter.

PS He is quite up there in age.

Thanks for your help

Answer
If he's quite up there in age then I think you may have a tough decision to make. He seems to be greatly suffering and if he's eating less and less and you've tried everything, I don't know what else can be done. She hasn't gotten better and if she is getting worse than it may be time, especially if he is old. I'm afraid there's nothing I can telly you, it may be time, especially since he's suffering so. It may the hardest thing to do.