My 8 year old had a molar pulled. She was on 2 separate doses of antibiotic about 2 weeks a part, during the surgery she also had a dose of antibiotic. A few days after the surgery I noticed her teeth turning yellow. After screaming and brushing her teeth myself over and over again, they are not yellowing due to lack of brushing. Her teeth went from white to really dark yellow in 1 week. What causes this? How can I get her teeth white again? Please help!