Period is late, but pregnancy test shows negative?

My girlfriend and I had some unprotected sex about a week and a half ago. She was supposed to get her period today, but it did not come. On top of that, she has had little to no usual symptoms she gets before the period begins. She has taken three pregnancy tests in the passed two days, all of which tested negative. Is it possible she is pregnant? Or is it more likely she will just have a late period? How should I proceed?
Asked Aug 05, 2017

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