If found blackish color on the nails, there are many things that should be suspected:
Hematoma.It should be suspected in case of previous trauma (hand squeezed, or terpentok)
Fungal nail (onychomycosis or tinea unguium).Can be started from the end of the nail and nail bed that can slowly lift the nail.
Melanoma is hidden.No blackish color on the nail bed which is located under the nail.Melanoma is actually a skin tumor derived from a cell which resides in the skin called melanocytes.Although it is not often, but in fact melanoma can occur in hidden places such as under fingernails.
To know the exact cause of the disorder, it can be examined KOH and culture (to make sure there is a fungal infection and rule out a diagnosis of melanoma).Healing fungal infections of the nail does take a longer time than other types of fungal infections, may last for 3-4 months .. Medicine suggested that oral medication.Being medicated ointment or cream usually less effective in the treatment of fungal infections of the nails, because it is hard to nail cream / ointment difficult to absorb.
Your concern about the possibility of melanoma of the nail can only be ascertained by examination of biopsy (taking part of the affected areas to then check its cells under a microscope).Of course it must be preceded by an assessment of the medical specialist and genital skin.You may seek the opinion of another doctor, especially if the black color becomes more widely although it has been treated with oral medication for yeast infection.