Q. How do i cite multiple short stories in a collection?

First you might want to check with your proffesor. MLA has gone to an 8th edition which is a sad shadow of its former glorious 7th edition. I have heard that some CSS professors are ignoring the 8th edition and sticking with 7th, so find out what version they want.

With that said, neither version addresses your question.

MLA 7th does show the format for a short story in an anthology. And because each story in an anthology is by a different author, then a citation is created for each story you would use. I did not see any reference to a book of short stories by a single author.

So, let us work with what we know and some common sense... 

a). I think I would create just one reference in your bibliography for the book (not individual references for each story).

b). Your parenthetical references are author and page number, so your reader will know how to find the source in your bibliography.

c).  That leaves us differentiating what story you are discussing, but that seems to be something that would be obvious through the creation of your text.

Example:

While White's story "An Australian Shepherd is Too Smart to Create Something Like APA" seems humorous by the title, it reveals a deep dystopian vision, an archetypically deconstructive mimesis, reinforcing a macro-Saussurean framework of langue and parole, that portrays an academic institution not dedicated to learning, but slavishly devoted to the proper indenting of a running header. In tone, it is far different from his humorous masterpiece "We Are All Doomed" in which the protagonist laments "we will be wishing it was just a zombie apocalypse" (89).

I would defer to your ENG prof is she/he has a different opinion.