I'm worried I have a fetal Doppler I was using it this morning and I feel baby move I put it by…

I'm worried I have a fetal Doppler I was using it this morning and I feel baby move I put it by there and I get the HB up to 145 but for like 25 seconds then baby moves I put the Doppler a little lower and on the sides of my belly button and it's reading 125- 140 BPM then my pubic bone I think that's my HB I hear there. I used to hear baby by pubic bone now I have to basically chase baby. anyone else have a Doppler? how's yours work? I'm 22 weeks