hello..thanks for the query
If you have had negative cultures/KOH examination of the scrapings ,fungal infection
might not be the cause .In that case Lamisil
might not be able to cure.
The black spots are a result of the ongoing inflammatory process in your skin.From the kind of lesions you describe , I would think of two possibilities :
: It is common for psoriasis to be present only as cracking of the feet with thickened areas/or red scaly patches.
2)Eczema : This might also present with fissuring of the soles and red itchy patches.
I would advise you to visit a dermatologist
when you have the active patches for a biopsy
of the same.
Hope this is helpful.Take care!