Thrush

My son keeps getting thrush! I have no clue why. He had it very bad for a few months and four doctors told us it wasn't thrush. Feedings were terrible and his tongue was covered in white. We saw a new doctor and she said he had terrible tongue thrush and prescribed us fluconazole. The white he had had vanished in weeks, and finally he was eating like abnormal baby. It cane back and she suggested no more pacifiers and sanitizing and boiling the babies bottles and nipples. We did so often and microwave sanitized every feeding. He also doesn't use pacifier. It happened again so she perscribed fluconazole once more. Now it's happening again and I'm so confused! It's so annoying and we finish the medicine and use it like we are supposed to! Is it on his toys and blankets?