Baby movement

Hey I am 19 weeks tomorrow and I am positive I felt my son move for the first time on New Years Day. I was laying on my stomach and it felt like something was punching on my abdomen from the inside, like little tapping. There was no question it was him at that time. My question is since then, I feel like I have felt like I feel him moving every so often. Sometimes I feel like a weird rolling feeling, almost like the kind of feeling you get when you’re on a roller coaster.... is this the “butterflies” feeling people reference?

Sometimes it kind of feels like gas but there’s no actual gas bubbles or gas production. And it’s only every so often. I imagine this is him. Usually when I’m sitting down or laying down.