First movement at 16 weeks??

Yesterday I noticed that when I lie down and be still, there would be a couple "movements". I never felt this before as this is my first. It kinda felt like a pulsating blood vessel, but not regular. It was almost at the pubic hair line on the left side of the uterus. Like a thump? It was only like 2-3 times and only when I was lying down on my back. And I could've sworn I SAW it, too. Is it possible it was the baby kicking, or am I just being dumb (wishful thinking)? I'm skinny btw if that has anything to do with anything.