Does anyone know what this is caused by?

Nicole • Mummy of 3💙💙💗 #4 due October💗
Every so often something bulges out in my abdomen it feels hard and I feel pressure. I wake up with it every morning, and every day it comes and goes throughout the day. When I rub it for a little while it either moves to the other side or goes away. I was thinking it's baby pushing his bum or head out or something but I'm 17 weeks is the baby still that low?