Upset in the natural balance of candida fungus living in the mouth causes thrush, usually as a result of the use of birth control pills, antibiotics or corticosteroids, according to WebMD. HIV infection, cancer, uncontrolled diabetes and hormonal fluctuations in pregnancy often lead to this imbalance, causing thrush symptoms.
When the balance of candida in the mouth spirals out of control, candida grows and causes symptoms of thrush, notes WebMD. Symptoms include creamy white, raised lesions on the inner cheeks, tongue, roof of the mouth, back of the throat, or tonsils. The lesions take on the appearance of cottage cheese, may bleed and are painful. If the lesions spread to the esophagus, swallowing is difficult and painful.