So I was lying in bed and noticed that my tummy started pulsating. Pulsating like a heartbeat. anyone else know what this is or experienced it before?

Sounds like baby is hiccuping! Baby may start to hiccup from 3rd tri onwards and it'll look like your tummy is quivering. I always laugh when I feel and see my tummy quivering! I can almost imagine how baby must be feeling in the womb