soooo scared

So I went in for my ultra sound and all they saw was a yolk sac and absolutely no baby and obviously no heartbeat. They said I could be 4-5 weeks along. They want me to take another blood test after today in 48 hours to see if hcg rises. If not I'm most likely having a miscarriage. They told me I may be earlier than they thought and this may not be a miscarriage though unlikely..
Has anyone had any experience like this?! Good or bad? I just bawled my eyes out and left to take my blood test. I go back in 2 days then depending on blood test another ultrasound in a week or so.