I have a ten to twelve week old beagle. We got her two days ago, and she has barely eaten or drank anything. She is very shy and distant, which with my experience with puppies isn't normal. She has diarrhea, and vomiting. We took her to the vet and they gave us medicines and prescription dog food but she still won't eat. In desperation (and I don't normally do this) we tried feeding her a hot dog, but she just turned around and went to her kennel. I don't know what to do I'm getting very concerned about her.

Was the vet aware of the vomiting and diarrhea or did this happen after your visit.
With a pup that young my first concern would be parvo.
It will be worth taking her back or getting a second opinion, before she reaches a point of no return.
Pups will go downhill pretty fast when they don't eat, not to mention if they have diarrhea and are vomiting.
In the meantime, you can try to keep her hydrated with gatorade or pedialyte, if she is able to keep it down.
I strongly suggest calling the/or another vet sooner rather than later.

Yes the vet was aware of the vomiting and diarrhea. She said she didn't think it was parvo.

Where did you get her, what kind of place?

What was the background of the dog

We aren't sure, we bought her off craigslist and the woman said that it was her neighbors dogs that had puppies and they just wanted to dump her off somewhere... she kind of acts like she has been abused...

Maybe that's causing it maybe she's distressed ask the vet if the background could be a problem

Abused and scared is one thing, she would likely scream. Yelp, and run from you.
The important thing today is the not eating, vomiting, and diarrhea.
She won't go very long like that without taking a turn for the worst.
Even if it isn't parvo, something is going on. What medicines did they give you?
How long has it been since you took her to the vet, and has there been any change since?
I really urge you to call them and let them know she is no better.

I'll second Lady Sams post. You need to get something in this pup. A young puppy not eating or drinking will not last long. You're looking at days before you have a dead puppy.

The background isn't important. An abused dog doesn't refuse to eat or drink. There is something physical going on here, not mental.

She will get dehydrated fast. You need to go back to the vet, or find a vet that will actually do something about this.

In the meantime, pedialyte to keep her hydrated. Follow the directions on the bottle, and yes, it's very safe for dogs. Cook some rice and chicken, see if she'll eat that.

But most importantly, get her to the vet asap. This can't continue.

Please keep us posted. I really hope that it all goes well. My 10 1/2 year old border collie cross died 2 weeks ago today. It started with a limp, then lethargy, and then no eating, but excessive drinking. Three days after he stopped eating we had to put him down. He was severely dehydrated, had lost a lot of weight (and he had extra weight to spare), and there was nothing more the doctors could do. He refused to eat. I managed to keep him alive as long as I did by force feeding him, but even that was thrown back up.

I don't want to scare you, but dogs can go downhill very quickly. I'd hate to see that happen to your puppy.

I wish you all the best.

Parvo isn't something to "guess" about... maybe another opinion (another vet... I'm disappointed that your vet would attempt to treat a potential parvo pup with food and medicines... unless that is her method of diagnosing parvo? ) will be more helpful. There are simple, fairly inexpensive tests available to fairly accurately diagnose parvo.
You, and all who handle this pup could be spreading parvo to all the dogs you contact. Plus, the areas she has been in are also potentially infective to other dogs, too.
As Lady Sam suggests, signs like this in a pup cause people in the business to think of parvo first thing. There are other similar diseases, but there are tests, as I said. It serves everyone to know when a pet is ill with this disease.
You are to be commended for trying to "rescue" this pup from people who apparently didn't want it anyway, but Craigs list is not the most reliable place to get a pet, and this is a major reason why... this pup and its mother possibly have not had the benefit of decent veterinary care prior to now.
If this pup doesn't survive, do not blame yourself... there was a time that almost all parvo puppies died in spite of all efforts to treat. Successful treatment is "iffy" at best even now, regardless of who does it, and how.