When I first felt her kick it was only when I was laying down for a bit. And as her kicks get stronger I've started feeling them more at different times and in different positions. I'm just a little over 20 weeks as well. I wouldn't worry too much. I thought it was odd at first too and had quite a few people tell me it was normal just because you're laying still and the position you're in. They'll eventually get stronger and you'll start feeling them when you're standing up.
my bby did this around 20 weeks im now 24 weeks n mainly still does but also kicks other times now
I'm 22 weeks and I find they kick mostly when I'm lying down. Sometimes when I'm feel I'm haven't felt them for a while I'm lay down to encourage them, it doesn't always work but it does sometimes.