Delayed Period, No Sex!

Hi. I will try to make this as blunt as possible. My girlfriend is EXTREMELY regular. We even calculate when she will be on and off her period and plan certain things around it. We have NEVER had sex, but participate in dry-humping/rubbing. I ALWAYS have a condom on, and she takes birth control. From her last period to now, we have done stuff like that 3 times. And I never cum around or near her. She finishes me off with a HJ and I spurt into the condom. We check for leaks in the condom everytime by blowing into it to inflate it. all 3 times there were no holes or leaks. However, right now she is about 5 days late. I told her that I think it is because we got into a HUGE misunderstanding at the beginning of the week, and the emotional stress may have caused it to be late, or that her irregular sleep patterns may have caused it because she wakes up at 6 am everyday to babysit to little girls. We have scratched and dug through out minds to try and figure out why she is so late, but nothing has gone wrong, no cum, no pre-seminal fluid, has even been close to the opening of her vagina. She took a test 4 days after her missed period and within seconds it came up negative, but we are still frightened. My parents are going through things and I have NO IDEA how i will break the news of a baby to them. But like I said, we have NO idea how this could have happened. And to rule out other things, no i never touched her after touching myself, she doesn't like mutual masturbation, and we have never done anything other than just rub against each other.

Your answer/help is GREATLY appreciated.
Thank you.