They are just more mobile now... its a phase and it happens all the time from about this age. Both my kids did that too.
But it will pass.
He's just changing and developing. Don't take it personally.
But, so in the meantime, with my kids, I just had to change their diaper anyway, whilst they are screaming, holding them down with my legs as I sat on the floor to change them, and giving them a toy to play with while I do it to distract them. Then, I tried to be real quick about it. Then it's over, and on their way they went.
Later, as they got a little older, I would enlist their "help" telling them "go get a diaper for Mommy, time to change...." and they would "like" to help. Then they go through the stage where once they start walking, they will actually run away... while laughing, thinking it's "funny" that Mommy has to chase after them and catch them to change their diaper. Ha, ha. Oh well.. .just another phase. Then, if not, then I would tell them if I don't change their diaper they will get "red" and get a rash... so they understood this and then would cooperate more...
It WILL pass though. It's doesn't last long.
no worries. It's just irritating for us. They scream at diaper changes, or at brushing their teeth, or at taking a bath, or other things. They just are learning cause and effect too.
My son does not like to change his clothes either... but so he will scream but I change him anyway. As soon as I am done, he stops yelling. We gotta change them... it can't be helped.
Good luck,
Susan