please help!

I've taken my little one to the doctor twice over this, she's 15 weeks old but he brushes it off as a little yeast and once her neck grows out she should be fine and he prescribed her something for the yeast but it's done nothing. have any of you experienced this with your little one? what happened?

***EDIT**** We kept her neck clean and dry before this even occurred and even more so after

***EDIT#2*** we do use organic coconut oil, never thought about neck cheese though (I'm familiar with the term) looked it up on here and see other moms experiencing the same thing and use Destin. Will give that a try, thanks ladies.