His Penis shakes inside my vagina

Okay I don't really know how to explain this but almost every time me and my husband have sex and he's inside me his penis shakes a little like I can literally feel it!! Idk if shake is the correct word to use here or maybe moves inside when he stops moving up and down. Has this ever happened with you guys? If so, why does it happen? Because it kinda freaks me out and that's the only thing I concentrate the whole time. Then we stop having sex because of that.

It doesn't happen a lot of most of the time it does and when it does I don't wanna have sex anymore lol