Very large white spot on tonsil. strep and flu tests negative. had mono 15 years ago. severe sore throat, body aches, chills. why spot if not strep?

Likely tonsil stone: There are debris collections called tonsil stones that sometimes appear on the tonsils. The majority of sore throats are viral including a variety of adeno-viruses, para-influenza virus among others. If it is not strep A antibiotics would not be helpful & you will likely self heal over time. You can consult an ENT about the stone.