No yolk sac or fetal pole seen:(

Went to the ER last night bc was cramping worse than I thought I should be they did blood work and my hcg was 13,700 (which is good) but when done ultrasound they found no yolk sac or fetal pole and found out I wasn't as far along as I originally thought. I'm only 5wks 3days doctor said it was possible that I'm not far enough along to show anything but could also mean it's not a good pregnancy has anyone else had this happen and if so did you have a successful birth??