The Girl I Slept With Is 17. Going To Be

The girl I slept with is 17. Going to be 18 in sept. Lives alone with her cousin. But we had slept together the night we met I never ejaculated. Then we slept together two more times after that and I did ejaculate but I pulled out both times. I did not wear a condom any of the times. So we only had sex a total of three times two of which I did ejaculate and pulled out successfully, well the last time we had sex was a month ago. As of today she is two weeks late on her period and doesn't know why. She took one pregnancy test before she told me and it came back negative. She then told me she was late and I got her two more tests and she took one the night she told me and one the next morning as soon as she got up and they we're all negative. So 3 negative tests after a month since sex. But she still hasn't gotten her period. I guess I'm wondering if I should I be worried she's pregnant? She said this hasn't happened to her period in like 3 years.