You're very likely to have candida overgrowth, which is the main cause of thrush. Anxiety has very little to do with it. Don't listen to your doctor, most physicians have no knowledge of how to cure candida overgrowth permanently. Diflucan alone will not cure it.
Candida overgrowth is a condition linked to many diseases, AIDS included. The main causes of it are Antibiotics
, poor diet, some pharmaceutical drugs, stress... When the candida that we all have starts to take over the good gut flora, symptoms like those that you have (and many others) start to appear.
A complete change of diet and the intake of herbs and probiotic foods are recommended to cure it permanently. Antifungal pharmaceutical drugs, although efficient at killing candida, are not recommended because they're often hard on the liver.
I suggest you visit the candida page on this forum.