no yolk sac

I am currently stressing out, got my ultra sound done, the sac is measuring 6 weeks 1 day and the fetus is 5 weeks 6 days, my levels are 14690. Is it normal to not see a yolk sac at that time? I have heard you should, the doctor thought she could see a heart beat but couldn't capture it, I am measuring to the day. I need some reassurance