LO is 6 1/2 months old and has had recurrent thrush in his mouth that I just can't get rid of. He hasn't had it in about 2 months but it's back again!!! GRRR. I have been using Nystatin suspension 4x/day when he has it but it must not be working properly. How can I get rid of this for good?

Any other suggestions?
I've heard of gentian violet and grapefruit seed extract.