Baby movements

I'm 36 weeks and feeling my baby moving regularly but very often she does this thing where she stretches her legs (I feel one on one side) and I can see and feel (what I think is) her bum, round and hard poking out on the opposite side of my belly. It lasts for 2-3 seconds and then she relaxes.

She does it when I'm resting but also when I'm walking and I'm worried maybe it's a sign that she is struggling?

This is my first baby so please I just need some reassurance that this is ok.

Anyone feeling anything similar?