Doppler question

Bowser • 🌈🌈 due March 2016
So last night I felt the baby hit my stomach, bladder and cervix all at once. Probably stretching. I have a doppler but I use it maybe once a week if even that.
So I checked and found a heartbeat on my pubic bone,
And when I was moving it another about 3/4 inches up and to the left. Heartrates pretty much the same.
I have never gotten two before so I know one is probably my placenta, how do I know the difference between?