Diaper rash from different size?

Yael • My baby girl is my WORLD

My daughter has suddenly started getting a constant diaper rash we can't beat. It started right before we switched sizes but usually if she got a small rash we'd get rid of it within a day. We just went up to 4+.....and this rash will not go away. Same brand, Huggies, but they're Huggies freedom dry.

Has anyone ever gone up a size and ended up with a rash that won't end???