Baby not moving??

liz • I’m Liz 🙃 Stay at home mommy to Carter Bentley born August 10, 2018💙

So I am 21 weeks pregnant today, I first felt the baby move like 2 days before I was 20 weeks. But the last 3 days I haven’t felt the baby move at all! I have tried lightly pushing on my belly, music, and no movement. I have a heart doppler and used it and I can hear the heartbeat. What could be up?