Might be a heat rash! Make sure to clean with soap under neck and dry it very well after a bath with towel
Looks like heat rash xx
I’m not sure but my boy had it last week and now it’s gone I put it down to his eczema although it may be heat related x
My LB has had a rash like this come up and when we took him to the doctors they said it was from his drool and gave us some cream to clear it up. The creams definitely working as it’s starting to clear again