Pregnancy tests all say negative, but girlfriend still hasnt had her period and shows beginning signs?

my girlfriend has taken a multitude of tests and all say negative, her period is late by a month and all her friends say "oh your period is just late" but i mean come on, seriously? i know how much of a waste pregnancy tests are now, but she has symptoms like, really hungry, sore , and she is a tad bit emotional, there are no girls i know that have had periods that late, and i know some women that have irregular periods. i would just like some help from this knowledgeable community and ask you people on yahoo if in your opinion she is pregnant or not, thank you