7 mo old SCREAMS at every diaper change

my son is 7 and 1/2 months old and this started about a week ago. he's in that stage where he's always arching around so it's a pain to change his diaper, anyway, but he's started screaming at the top of his lungs (EVERY time. even if he's in a great mood) and sometimes keep rolls so hard it's almost impossible for me to change him. I literally have to lay my leg over his chest (gently, of course lol) . this happens no matter what mood he's in. i dont believe its teething pain as his first two teeth already just pushed through and he wasn't doing this when he was in obvious pain. but I'm open to anything. is this a phase??