Eating watermelon in small quantities has the effect of clearing away heat, and generally does not cause the cause of fire, the sore throat may be caused by cold.

Suggestions:

Only a long time to eat a lot of watermelon can cause the situation of fire, but by chance you eat once, it should not be. It should still be the manifestation of upper respiratory tract infection caused by cold. You can take the oral solution to clear the heat and detoxification.