Can my gyno tell if i'm sexually active?

No: It is a misconception that there is an intact hymen or membrane that is always broken and is tell-tale evidence that a woman/girl is not a virgin. Not everyone has one or it can be stretched or broken through non-sexual activities: stretching, horse back riding, gymnastics, tampon use, etc. But it is EXTREMELY important that you share this information with your doctor; it will be confidential.

No they can't: Girls are born with a hymen that blocks part of the vagina. It is a thin membrane. It is often broken with a first sexual encounter, but can break for other reasons, such as an impact from a bike seat. Your gynecologist can tell if this membrane is still there, but not why. Unless you have caught a disease, such as warts, your gynecologist cannot tell by looking if you are active.