12 days late!

Samantha
I am worried that I might be pregnant for obvious reasons but I took a pregnancy test on day 7 of my late period and it came up empty. I was on birth control for about four years and I stopped taking it about three months ago. My period was normal the last few months. Also, I just quit smoking cigarettes. 
Has anyone quit smoking cigarettes and it affect their period?
I might be under stress because of the withdraw or whatever but I quit like 2 weeks ago.
Heeeelpp!