need your opinions!

Caitlin
Hi ladies! So I am just about 10 weeks and heart and saw baby heart beat on the 3rd (156 HB) and rumb was 21MM. Everything was great. 
I bought a fetal Doppler and couldn't find the HB this evening. I'm wondering what experience you have? Should I be worried? I had a miscarriage at 6 weeks in August, so I've been super worried. 
What are the chances of miscarriage after you've heard and seen a strong heat beat and everything looks good!? 
Any insights!?!?! Please help!