Is it typical for per-diem job?

Hi All,

I recently got a job as a per-diem CNA at one of the healthcare staffing companies. After the interview/orientation, they gave me some shifts ( 5 days a week, 8 hour shifts) but they've canceled my shift three days in a row. When I call them the day before and confirm my schedule, they tell me that no change has been made. However when I call them a few hours before my shift starts, they tell me that my shift got canceled.

I'm just curious if it happens sometimes. I would not be so worried if it happens once in a while, but since it happens three days in a row now, I'm getting a bit nervous. Please give me any info/thoughts/ about this. Thank you.