My 4 month old has had this rash under his neck for over a week now…

Help please!  I clean it 2-3 times a day, dry it and apply aquaphor. I’ve also tried Tubby Todd. Ive been changing his bib/clothes more often when they’re wet from spit up/drool. I’ve already been in contact with his pediatrician who said keep doing what I am. I’m going to reach out again tomorrow. It was getting better then started getting worse again over the weekend. What has worked for you? What am I doing wrong? Feeling like I’m a terrible mom

(Shiny is not wet, it’s aquaphor)