Suggest Treatment For Plantar Facetious In Feet

I have tiny holes on the bottom of my feet. It seems to be more prevelant in the warmer months. I went to a dermatologist after researching online and we agreed it might be a type of fungus. I was prescribed a gel to put on them but it didn't work. I went to the Podiatrist and was diagnosed with Plantar Facetious (sp)? Anyway, I asked him while there about them and he just told me to keep using the gel. He seemed to disregard that particular issue. Any ideas on what they are, what causes them, and how to get rid of them? Thanks so much
Susan