Pregnancies vary. I don't think anything is wrong. Baby is obviously growing. That's great that you are having this experience early. With my first, I don't think I saw the "wave" until week 28 or so. It was never ending after that.
I don't think it is too early for you, what an awesome sight!!!
I felt the EXACT same thing yesterday! Only I didn't see it from the outside, I felt it with my hand though, because I wasn't expecting it, I didn't look, then for about 5 minutes after he was kicking! :]
Thanks ladies it really is amazing to see and feel him moving around in there.