I Went to the ER last night due to major pain, found out I'm 5 weeks and 5 days pregnant they only found a sac?

Don't worry my dear. It is very common to only see the yolk sac at 5 1/2 weeks gestation. You cannot see the heart beat until after the 6th week generally, and then I think the 7th or the 8th week, you can see the embryo. So do not fret. Everything seems to be going well. And since the yolk sac in in your uterus, it is almost 100% guarenteed that you are not having an ectopic pregnancy because the yolk sac serves as the placenta for the first few weeks to nourish the growing fetus.