See your doctor. You don't say where you have it so depending on the region see your dentist or physician so they can prescribe the appropriate medication.
Thrush=fungus. Thrush is relatively common in infants/children, but not so in health adults unless something happened. Such as recent use of antibiotics, infections, steroid uses (such as those for asthma/copd/allergies), or immunosupressed states such as hiv, cancers etc...So, check with your doc. If it is thrush, it can be easily treated, but this requires a prescription from your doc... Good luck.
Thrush in an adult? You should be seen by a doctor and tested for immune deficiency states, including hiv. Normal adults who are not diabetic or taking antibiotics should be having thrush without some underlying reason. Go get evaluated.