Diaper rash 😕

Eva

My son is 17 days old , his bottom is really red. I change him right away every diaper change so it’s not that he sits in it. I started with Huggies diapers and then for a couple days started using parents choice (Walmart brand) but then I went back to Huggies if that matters. I’ve been applying Desitin but if anything it looks more red than the last 2 days.

What can I use to make it go away?

Why does it happen and how can I prevent it? TIA