Home doppler 12w 3d

I got a home doppler a few weeks ago and now that I am 12 weeks I decided to try it out! The last two days I have been able to find the heartbeat after a little searching and tonight I was unable to find it :( hoping baby is just hiding but can't help but worry! Anyone have this issue before? Just want some reassurance it's normal! Haha worrying mommy!! 😩😩