I had that problem too, I took high dose zinc for it and all cleared, b as well. I think that was candida on me. I stopped the zinc and multi ( had the b ) and was fine ( 6-8 months ) until just lately have been detoxing metal so it came back but slightly, nothing like before. I added them back and it is clearing up. I also now have morgs in my lips. I got it out of one spot and am working on the other. It is completely different than the corner of the mouth sores. I think I do not absorb nutrients well for obvious reasons...