Worried all the time! help!

I go Monday for my first ultrasound for my rainbow baby. I am completely worried all the time. I can’t stop thinking that I’m going to go in, and they are going to tell me the baby doesn’t have a heartbeat. No matter what I do I can’t stop thinking about it. I get randomly nauseous, but not like I did a 2 weeks ago. I’m exhausted, and my nipples are so sore. I can’t stop thinking in my head I’m having a miscarriage because I’m not as nauseous like I was 2 weeks ago. That’s how I noticed something was wrong when I had my miscarriage. Anyone have any advice to help me? Before I come more of a wreck than I already am?