Heart palpitations

Kristin • Married with 3 beautiful babies. 💕💙
I've had random heart palpitations for a long time. It was very infrequent and just once for like 5 seconds then gone. I didn't have them with my other 2 pregnancies but this time I've been having them a lot. Like all day for a week then they went away for 2 days and has been back about for a week. They tested my thyroid & numbers came back normal. What else could it be? Is it normal for it to happen so much? And why didn't it happen with my other 2? I'm just starting to worry