What Causes White Coating On Tonsils Post Treatment For Tonsillitis?

Hi I am a 21 year old female. I had a lump on my neck that appeared I wasn t sick with it or anything until 5 days later I had a really mild sore throat but I found it hard to swallow it was like my throat was swollen. Went to the doctors he said it was lymph glands and tonsillitis he prescribed me amoxicillin I finished the pack but my throat is still hurting when I ve looked I ve got white stuff coated all over my tonsils and the roof of my mouth is orange. What is this?