when you get to basic training they will give you a pregnancy test. every girl gets one. it is just to make sure because alot of the girls have sex right before they leave. then anytime you get sick they also give you one.
if you are pregnant they will send you home with the option to return once the baby is a certain age OR allow you to end your contract with the military.
don't worry, this happens alot. when i went threw basic there was a group of girls who turned up pregnant.