If you're worried, you can contact NHS 111 out of hours and on weekends. They will ask for symptoms and work out the next steps, and provide advice.
I’d get it checked for yeast if it’s still there in a couple/few days
@Kell he’s formula fed though? He’s been having the same brand formula since birth.
Looks like an allergy
Yes mines had something similar from where milk was gathering. I just double check clean and dry now..GP would also prescribe an anti fungal but should go away on it's on nonetheless.