Hello mommies ?☺️ My little girl is already 4 days old, I have a flat …

Hello mommies ?☺️ My little girl is already 4 days old, I have a flat and retracted nipple on my left breast and my daughter doesn't want to take it, plus my breast has become big and her mouth is very small, she only eats from the right side where there's some nipple. The left breast starts to go numb, they advised me to express by hand but still something needs to be done so that the baby starts taking it and the left breast. I don't know what to do, what would you suggest? ?