Can braces cause this?

I just got braces yesterday, and when I flossed, I had no problems. When I flossed today, my gums bled. I only got the brackets and wire on the top, and when I flossed my bottom teeth, they didn't bleed at all. So I don't think the cause of it is gingivitis. Can the force of the braces cause your gums to bleed? I would call my dentist, but they aren't open on the weekends.