oral thrush

My little guy is now 2 1/2 months old. He's had thrush since he's been about 4 days old. We cannot seem to get rid of it. We've tried nystatin, diflucan and gentian violet. The nystatin did nothing so we went on 4 weeks of diflucan. In that 4 weeks he got rid of it for a day and then it came back. Next we tried gentian violet which worked but then three days later it came back. 
Is there anyone else out there who has suffered through this like us? My baby is the sweetest boy ever but has horrible pain caused by this. Please help!