Baby disappeared?!

Rachel
I am 9 weeks and have had 2 ultra sounds where I was able to see the baby and heart beat (one at 6 weeks and one at 7 weeks). Today my dr was not able to find the baby via ultra sound nor was able to hear a heart beat and she said it could be because I have a tilted uterus. She also has an older machine than what was used the first two times. Has this ever happened to anyone? Fearing I lost the baby?!