Fusarium infection in infant/newborn's toe, please help!!

My son was born almost two years ago. Since birth he has had one, as we call it "funky toe". Every month at his checkups I would ask the Dr about his toe and she would just say it was just a "funky toe" and that sometimes happens. at his 18 mth checkup I told her I was concerned that it was getting worse and she referred me to a Dermatologist. They took a sample clipping and called back, saying it was a fungus (did not say what or HOW he got it) and prescribed some meds. (two topical creams to be used twice a day) He is now 22 months old, and the toe looks just as bad, if not worse (there is NOW a black small spot). I called the dematologist again, and they called back saying he could take Lamisil, but it could damage his liver.  I asked WHAT the fungus was and she said it was Fusarium, and they didn't know how he got it. I am not prepared to put my child at risk for liver damage by taking Lamisil, but what are his "risks" if we don't? Can it spread, can it ever go away, can it make him sick or do permanent damage/harm to him, how did he get it, was he born with it, could I have some kind of fungus in ME that caused this?!?! All of these questions I asked, none were answered, well they answered "We don't know".  What can we do?!?