Hi, So Me And My Girlfriend Had Protected Sex On

Hi, so me and my girlfriend had protected sex on December 20th and the last time she got her period was December 12th. She is 16 and she's always had irregular periods sometimes she gets them every 2 to 3 months. It's been about 2 months and a week and she hasn't gotten her period but she has not had any pregnancy symptoms. Is she not pregnant?