Worried about baby (18 weeks)

I last saw him at our 16 week gender scan, and he was doing great, we have to wait until 20 weeks to see him again. I haven't developed much of a bump at all, just a bit of fat around the lower tummy really. And I haven't felt him move yet at all. I'm worried that he's not okay in there... I know I'm probably worried for no reason, but could someone please reassure me that they felt the same but everything turned out fine?