Terrible diaper rash + whole milk???

My 16 month old has been having a terrible diaper rash for about a week or so and it just won’t quit 😭 The only change he’s had in his diet is a cold turkey transition from breastfeeding to whole milk over the past month. I was hospitalized for 26 days and on a persistent dose of antibiotics and narcotics (that’s a whole other story but I had a near death experience essentially so please don’t judge me - it genuinely broke my heart to stop BF). Anyways, could it be the whole milk causing this diaper rash? He’s always used the same baby wipes and same diapers. And as I mentioned his diet is completely the same minus the whole milk. The diaper rash even has two little raw spots. He isn’t sitting in wet or poo diapers for long periods of times either. We’ve been using boudreaux’s butt paste max strength religiously. Letting him walk around naked. Any suggestions?! Help my poor bubbas booty 😩