rashes on baby's face

Hi there. Just wanna ask some help.. My two-week old baby has rashes in his face.. Some people said it's normal and it will go away soon without nay treatment.. Buti i still decided to consult a pedia.and according to her, my baby has allergy to the food that i eat while breastfeeding, so she told me to have a diet. However, I noticed that the rashes disappear and reappear even if im not breastfeeding him. So I doubted what the pedia said especially that she didn't do any laboratory test for this allergy.. Any advice or similar experience?