Do you think my girlfriend is pregnant?

ok well me and my girlfriend had sex about two and a half weeks ago..well she hasnt had her period since and she usually gets it around a day or two ago..she is all freaked out because she thinks shes pregnant..but I used a condom ans so I dont thynk so..I just think her period is late..I atleast got her to calm down and relax until we are for sure..any suggestions do you think she could be pregnant I know theres always a posibility but im prty sure she isnt thanks a lot

maybe stress, stress causes a late period. take a test thats how she'll know.