Questions about seeing the gynecologist?!?

Ok so I've always heard that once a girl turns 18 she needs to go and see this doctor. But, my friend whose 17 was panicking cuz she said her mom was gonna make her an appointment and we figure the doctor can tell whether or not you've had sex. Her parents dont know, and now I'm freaking out cuz I just recently lost my virginity to my bf and we've been having sex and I don't want my parents to know, esp. Since he's 24 and my parents don't even know we're dating!! I asked my bf about it and he said the doctor would keep that confidential. Is this true?!