im so sorry to hear that, i do know how u feel, it happened to me with my son who is now 3 and this preg, i went for my ultrasound they found a sac but no bub, i went back 2 weeks later and there was a bub and heart beat, sometimes our bladder isnt full enough or in my case my uterus is retroverted which makes it a lot harder to see bub untill its much bigger,
but just try to keep positive i know its hard and i pray that ur little angel is just fine