It can be leukoplakia White or grayish in patches that can't be wiped away...or tonsillitis,oral thrush etc....it should be examined properly and treated properly...Drink plenty of water,eat soft foods like cooked cereal, mashed potatoes, soft fruits, yogurt and soft-cooked eggs...give adequate rest to your body..Avoid spicy foods or acidic foods...Gargle with warm salt water..Consult nearest ent surgeon they will do the needful.