Is there a way that a doctor can tell I'm not a virgin?

My friend told me that at my physical the doctor pushing down on my stomach is to tell weather or not i'm a virgin if I don't tell my mother/father. Is this true?? && If so what should my response be when they push down on my stomach?? Also, I have been sexually active for a good 2.5years and I have only told the ppl I have had sex with and my sisters. I really am scared to tell my mom. I am 16 and I would love to know how to go about this. Thank you so kindly