My Pig Wont Eat!! Please Help!!!

Question
I noticed Monday that my guinea pig wasn't pooping, at first I thought she was constipated, and tuesday I brought her to the vet.  He gave injected some fluids and gave me this stuff called Nutri- Cal to feed her three times a day.  This was yesterday and, if anything, she's gotten worse.  Her diet normally consists of timothy hay, timothy hay pellets, a small amount of oats and fresh fruits, as well as the occasional treat.  I'm really worried about her, she won't do anything, but sit in her little hideout.  Her teeth are fine and she does not suffer from hair loss, she just won't eat.  On Saturday I got a dwarf hamster and I was wondering if my pig might be jealous of her.  Last night I moved the hamster's cage out of the room my pig is in, but I'm not sure if that has made much of a difference.  I have been paying extra attention to her, she is a single pig and does not have a partner because when I got her I wasn't ready to take on two and was planning on spending lots of time with her (not that I haven't).  The hamster is healthy, and eating fine, so I don't think my pig contracted any disease from her.  So my question is what's wrong with my pig, and what can I do to help her?  How soon should I go back to the vet if she doesn't get better?  I'm at my whit's end, and have been up with her the past two nights until 1 o'clock in the morning.  Please help!!!!!!  

Answer
Have you been hand-feeding her? http://www.guinealynx.com/handfeeding.html
Are you feeding enough vitamin C? as well? I'm trying to guess at what could be wrong and the only thing I can guess is she is having an upset stomach or constipation and maybe the vet can give her some antibiotics.
Keep me posted on how things go.