S.T.
i totally disagree with karin. confronting her and dragging her in for tests will make her feel disrespected and as if her trust has been violated. this is a tender situation and should be handled with tact, love and a positive attitude.
you really can't make her open up. this is a privacy matter, and it's no reflection on your relationship with her that she may be less than forthcoming about it with you. it's not likely that your reaction will be 'yay!', after all.
trust that her basic good nature and your basic good parenting underlie everything that's going on here.
i do agree that driving is a great place to bring this sort of subject up. because you're both facing forward she won't feel interrogated. rather than *asking* her per se, that is having a conversation that involves her feeling pressured to answer, you could open it up in a 'once upon a time when i was a girl' way, telling her how you feel without ever placing her in a position where she feels cornered. allow silence if that's what she gives back, just keep it a warm, comfortable silence. you want her to feel confident about coming to you with questions or concerns, not pressured into a confession. tell her that you know she's wise and educated enough to realize that the pill won't protect her from STDs, and that condoms must be part of today's sexuality, no ifs, ands or buts. if you think she's too young right now, tell her that honestly, but with compassion and understanding for the possibility that she and her boyfriend are in love and trust each other enough to have proceeded. that you love and support her even if she is having sex and you wish she weren't.
you handle it by making yourself realize that in some ways your daughter is moving into young adulthood and you can't control her every move. you can tell her frankly that you wish she wouldn't, but imposing martial law and forbidding contact will have the opposite effect from the one you want.
i remember coming upon my older boy and his First Great Love entwined in each other's arms when he was supposed to be on the couch. i stood at the foot of the bed and held each of their bare feet and informed them that i knew they loved each other and were responsible, but that cara's mom trusted us to have her sleep alone at our house and that was exactly what i expected them to do in the future. that they would just have to sneak around to have sex, just like everybody else.
they were amused, appreciative of being treated like adults, and from that point on very respectful of the house rules.
:) khairete
S.