Not every woman has a hymen in the first place, and they can be eroded by everyday activities as well.
No-one, not even a gyn, can tell if you've had penis-in-vagina sex (or if you inserted other objects in your vagina for that matter), unless it was very recent and you have sperm in/on you, or vaginal tears.
This question and other common ones are answered by Scarleteen here: http://www.scarleteen.com/boards/faq.html
I guess a current STI with genital symptoms would also be a giveaway. But apart from that, no.
But dreamydancediva is right that it's good to share all information with your gyn so that s/he can treat you properly and give you STI/STD screens. No doctor can help you properly if you don't tell them your history.
[This message has been edited by Londongirl (edited 06-02-2004).]