Weird pulse feeling in stomach

Hey ladies! I'm 28 weeks pregnant and I keep getting this weird feeling like a heartbeat in my stomach. It's like a fast pulsating movement that happens about 2 seconds a part. It feels too fast to be a hiccup, happening too close together. And too slow to be a pulse or heartbeat, I've timed it with my pulse and my pulse is much faster. It's so weird!! It can last for like half an hour. Anyone had a similar feeling???