Baby wiggles??

I don’t even know how to explain this😅 since yesterday night, (could have been going on for longer, he doesn’t tend to lay on us to sleep anymore) when he was laying on his back on me, I’ve noticed my 5 month old have some sort of spasms? Wiggles? Rocking his hips back and forth? I don’t even know. It happened a couple of times.

I’m feeding him right now, his back against me like usual and hes been doing the same for the majority of the bottle, so like 10 minutes? The movements seem involuntary too. Any ideas?!😅