I Am A Divorced Mom. I Took My Son To

I am a divorced mom. I took my son to the dentist for a filling on Friday and then he spent the weekend with his father. When I picked him up this afternoon He had a large sore on his lower lip. I took him to a clinic and they said maybe he fell and bit it. Since the visit ... it looks like it is spreading and he now has more sores on his face below his lower lip. What should I do?