Is There Any Way To Prove Absence Of Sexual Activity?

Hi, my name is Andrew Price. I am stuck in an impossible situation it seems. The Mother of my girlfriend strongly suspects she and I to be having sex although we have not, and she has decided she is going to schedule an appointment with a gynecologist in order to prove that theory. The problem is that my girlfriend is not a virgin and has not told her mother. So even though we have not had sex she will believe I was the one who took my girlfriends virginity. Is there a way to prove medically that we have not been having sex?