worried

Today April 17th I had my second ultrasound, from what I was told I am 7 weeks from my last period (although my last period was a little irregular). So today when I went in my hcg levels are 8,456 but no heart beat yet, they measure the baby at about 5 weeks 3 day. The first time I went I had gone into the ER for this cramp near my groin area/stomach that was making it hard to walk. No bleeding. On Saturday April 15th they couldn't get the heart beat that day either and she measured me at 5 weeks 1 day then. They said that the baby could just be too small still. What concerned me was that the doctor today said she didn't see much growth and that baby's are meant to grow super fast in first trimester.  I'm just so worried, I just wanted to write this out. I'm just praying and hoping everything is okay.