J.S.
We have had the same problem. 2 things have helped.
1) gentian violet. it is a dye that is used as a fungicide on the skin. It can also be used for thrush. look it up on the internet and you should find exact directions. most pharmacies have it and you don't need a prescription.
2) my daughter had it behind her ears and i think it kept reinfecting her mouth which infected me too. I put the violet behind her ears too and haven't had any thrush since.