Stress Fracture

I thought that I had sprained my ankle about a week ago and finally broke down and went to the doctor yesterday.
They are treating me for a stress fracture in my right ankle, put me in an air cast, and on crutches for two weeks to let it rest.
My question is………….. Do I really need to use the crutches?
I work full-time, as well as go to college full-time, and trying to get around on crutches while carrying 20 pounds of books on my back is just too much.
I had been walking (or hobbling would be a more appropriate description) for the last week on it anyways, but I can tell a difference with just the air cast.
I still notice quite a bit of pain from walking, so I’m just wondering if the crutches are absolutely neccessary or should I call my doctor back and inquire about some sort of shoe she offered me as well?
Thanks