Home Doppler .. Now I'm worried! Ugh

Megan
I have had two ultra sounds where I heard my babies heart beat
6 weeks-129
8 weeks-171
I decided to purchase a home Doppler to ease some anxiety. Today I tried  it twice and I couldn't find anything close to 171. 
Now I'm nervous.. Not sure why I had morning sickness and exhausted all day but for whatever reason now I'm worried.
Give me some input. Maybe I am too early to try it at home? Should I call my OB tomorrow, maybe I am just over thinking, overly worried for nothing? Ease my anxieties please girls! Xo