my almost 4 month old newborn always cries when I change his nappy after he's done a poo!

What can I do to stop this he literally screams the place down I've tried calming him by singing , talking putting cuddly toy next to him but nothing works I try to do it as quick as I can but it's so messy down there! And I've also pulled a muscle in my back so can't go much quicker 🙈 any advice? What settles your baby for his nappy changes?