My Gf Is 17 And Had Brown Spotting On The

My gf is 17 and had brown spotting on the 30th day of her cycle when her period was suppose to come. We have had safe sex for the past 2 months only using condoms. She feels 100% fine. However when this happened she had an upper respiratory Infection amd was taking antibiotics. She is now 1 week late and doesn't know what we should do