Yesterday we were at the hospital. The doctor said that there's mold i…

Yesterday we were at the hospital. The doctor said that there's mold in my son's mouth and needs to be treated. We're on mixed feeding and it's important for me to keep breastfeeding. But the doctor said I need to switch to lactose-free formula and remove the breast. I think it's cool to switch both the formula and breast immediately for the baby's digestion. And how do I then switch back to regular formula? It's not good, right?