The stories here have been very reassuring! Thanks for the well wishes. I'll update tomorrow after I visit the doc and see what the ultrasound looks like.
One thing I forgot to mention--I've had other pregnancy symptoms (tired, sore breasts) but no morning sickness. That plus the bleeding has made me apprehensive about something going wrong. But, I will stay as positive as I can and hope the pregnancy is not in danger and the bleeding will resolve.