Squirming for sleep

I’ve got my 16 week old into a really good sleep routine - but he’s always squirming! He arches hjs back and cries non stop while being held, and keeps screaming being led down. We have him in a swaddle as he moves his arms so much he wakes himself up (this has helped him go into a deep sleep) but I don’t know what this means?? Anyone had this??