Prego or Stress?

Katie
Update: Still no Aunt Flo, really starting to flip out :(
Had unprotected sex on Dec. 10. I started my peroid like an hour before. He pulled out and I got Aftera within 36 hours after. But..I'm two days late and freaking out. I've been sick, as well for about a month and a half. I guess my question is, could I be? Or am I psyching myself out?