Diaper rash due to whole milk??

So I recently transitioned my one year old to whole milk and it was fine at first but now I’m noticing some bumps on his inner thigh so I put some diaper rash cream which usually clears up any bump or redness immediately (he’s on a special diaper rash cream that he’s been on since birth bc others always gave him bad reactions) ok so back to it has not helped which is so odd he has more bumps and it’s spreading to his butt cheek now and it’s red. I touch his little cheek and the bumps to see if there’s any pain and nothing he’s bouncing and rolling around laughing like normal which makes me think it has to be the milk. The only other new thing is I give him fruit juice sometimes now. Maybe it’s too sweet? I water it down but idk. He’s had an allergy test and they said he doesn’t have a cows milk allergy so I really just don’t know. I’m a first time mom someone please help