Unless you had a transvaginal ultrasound, you won't see anything until aroun 8-10 weeks. You can see a sac around 4 weeks but only with a transvaginal ultrasound. I wouldn't worry too much if I were you. You may be earlier along than than you think. The bleeding could be from a common thing called a subchorionic hemmorhage. I bled at 5 weeks with my first but had a transvaginal ultrasound that detected the baby, the heartbeat, and the hemmorhage. She's a healthy 21 month old now. With this pregnancy, I had a transvaginal ultrasound at 4 weeks (to determine pregnancy). They saw a sac but no baby. My hcg levels were normal (high) so a few weeks later I had another ultrasound that found the baby and the heartbeat. Again, you may be earlier than you think and that's why the ultrasound didn't find the baby! Good luck!!!