My girlfriend is on birth control and was supposed to begin her period on Sunday, December 7. She didn't get it, and we had sex on Tuesday night, December 9. She still hasn't had her period, but she has the symptoms, including light cramping, sensitive breasts, chocolate cravings, and feelings like she is going to have it, but it doesn't come. She took a pregnancy test today, but it came out negative. Does anybody have any ideas? Please help, we are very nervous.