sexually active can't tell doctor

okay so I'm 17 and my mom is very against me having sex but I have been with my boyfriend of two years in secret. I have a cardiologist appointment tomorrow, will they ask if I'm sexually active? If they do, how bad would it be for me to lie? I know I could tell my mom not to come in with me but she would see through that immediately and accuse me of having sex and I just really can't deal with that stress right now.