Everyone is different some show sooner then others! I'm pg with my second and didnt after showing unroll well into my second trimester! Is this your first? Alot of times people show later with their first! I wouldn't worry about it.
Have you had any prenatal care? The nurses check for heartbeats
Im 41 weeks and I didn't get a bump till 6 months pregnant and even then in my maternity pictures at 37 weeks they had to position me in a way so that you could see my bump! As far as your baby is concerned if you don't feel like your going to the doctor to hear the heartbeat enough you can always buy an at home monitor, that's what several of my friends have done to ease their own nerves