Why is AF playing peek-a-boo?

We were out to dinner on Thursday night and I felt like I was going to start AF, and I went to the bathroom, and there was the normal, telltale streaking that signals the start every month. I put my DivaCup in and worried (since this is my first month using the cup) that I'd have too heavy flow or something. But...later there was nothing. Next day...nothing. Saturday nothing, Sunday nothing. I've had SOME mild cramping but nothing major.

NOW...I know what you're thinking. And it would be possible except that DH has a vasectomy that has worked for the last 5 years, and we haven't had a bunch of relations this month because I've either been sick, too stressed over a major planning event, and my MIL is here for the month.

What gives? Could the stress have totally messed this up for me? My boobs hurt and I am so bitchy I just can't WAIT to start my period!