What Causes Rashes Around The Cheeks And Back Of The Ears In An Infant?

my daughter is 5 weeks old and has developed a rash around her right cheek and as far backas her ear, we had previously put it down to "Milk rash" but today the rash has spread up to her forehead and has made her ear very dry and flakey. Could you tell me if this is normal or if I should take her to see a proffesional? thank you