Pregnant or not? HELP!!!!?

My girlfriend has a regular period..3 days and heavy. Well this month she has been having pregnancy symptoms such as nausea, frequent urination, food cravings and avoiding foods she loves, mood swings, and shes tired more than usual. Her period was suppose start Wednesday but Tuesday night through Wednesday afternoon there was light bleeding then by that evening there was no bleeding..She started bleeding a little bit more today but not much at all. Shes took a pregnancy test this afternoon but it came back negative. WHAT COULD IT BE?!?!