You all know, and as this seems........It is a ...what done is done!
Now we should try to help the op so that this little pup will get the best start available to her under the circumstances.
Yes the pup should see a vet, but lets also help inform the op what he/she can do until then.
Get some Esbilac puppy replacement formula and feed that, no milk like people drink. Buy some good puppy food and moisten it with water or the formula, maybe even a little canned food. Start with several very small meals per day.
A very safe dewormer that is available over the counter has the active ingredient "pyrantel pamoate" just follow the directions for the puppies weight and it should be given approx every two weeks, until the pup is about 12-14 weeks old. First shots should be started at about 7-8 weeks depending on your vets reccomendations.
A puppy this young will not be learning the neccesary social skills from its mother or littermates. Such as bite inhibition and honoring another animals food. Don't be surprised if your pup has "social problems" later in life.
Please get vet checks, regular dewormings while young, and feed the right foods....... there is a wealth of other info in this forum that could help you as well.
Good Luck with your pup and I hope you continue to ask questions to help you along your way......
Best wishes.