Late period, never late, help!

I am 4 days late, and freaking out I might be pregnant. I've had none of the usual signs I am going to get my period, and me and my bf had sex during my fertile period (9% chance). 
We use the withdrawal method, but I have a feeling he didn't pee before we did it the 2nd time. I have been super stressed this month, so I'm hoping it might be that delaying my period? 
Has anyone had any experience with stress and late period, when they are usually regular?? 
Help please!