When should you see a sac?

Hey girls I took at home pregnancy tests and they both showed both lines right away I went to the hospital they think I’m 3 weeks pregnant my last period was on the 22nd of July but my periods are very all over the place. I had some spotting on the 14th and that’s it tbh all my symptoms right now are period symptoms they took an ultrasound but there was no sac also my hormone level is 1053 I’m just really scared if there should be a sac already I’m making an appointment for my doctors tomorrow since it’s a holiday today