How do I know the baby is okay between appointments?

I'm 16 weeks with my first & all of my symptoms have disappeared except my back pain that started at 14 weeks (it's been off & on, not consistent). One of my good friends was due 4 days before me & she had a miscarriage three days ago. Ever since I've been so on edge. I thought it was pretty much impossible this far along but now every little symptom I get scares me. My next appointment isn't until the 27th of July. How do you know if your baby is okay between appointments??