Its the same way for me at 22 weeks but I am not too worried about it. Baby is still small and has room to move around. And now with baby sleeping it should be fine. Soon enough we will have the crazy movements im sure.
He's probably up moving around while you're asleep
Be mindful that they do sleep. This one could sleep more then the others! I wouldn't worry too much, but if you are really concerned call your DR! Good luck.