schizophrenic coffee joint

I'm writing my first real short story. One that I actually intend to finish. I've come up with two characters who are distinct in my mind, but fuzzy on the page. I am having the worst trouble trying to come up with a way to set up a back story for my female character. I don't want to go so into detail because I want to keep it under a certain amount of words. I have been writing this for about 3 days straight and so far I've got the plot all planned out. But I am so critical on my writing, I fear I may get annoyed or bored and shove it to the back of my freakish mind. I am attached now to this story, so I think I will really try to make it work. Maybe I like the challenge.
Writers are crazy. That is my theory. We have to be slightly insane.
If I ever feel lonely or upset with reality I go hang out with my characters that have strangely become more real than I ever expected.
Help me Hemmingway....
Well then, back to work. MUST FINISH.
Ahhh....the sweet sound of fingers tap-tap-tapping across my keyboard..
Any words of wisdom would be greatly appreciated, as always.