Help, can't stop crying and worrying

Emma • 19 mo twin boys 💙💙 7mo baby boy🤰🏼 baby #4 is a GIRL 🎀 on the way!
So I know a lot of people will probably say just relax don't think about it! But I'm really struggling! 
I'm between 5-6 weeks pregnant and have my first scan (dating scan) in 10 days. I can't stop crying and worrying that there won't be a heartbeat! I had a miscarriage at 6 weeks in February and was pretty upset! As anyone would be.. but I can't get it off my mind! I'm so scared that I'm going to be disappointed again!
I have great HCG levels and no bleeding. Have sore boobs and no appetite at all. So it seems I have pregnancy symptoms! 
Is it common to have a pregnancy progressing normally and then see no heartbeat? Just want to hear some experiences and knowledge.