Hello,
From the symptoms fungal infections of the nail need to be ruled out. In onychomycosis(
nail fungal infection)
nail plate can have a thickened, yellow, or
black appearance. The nails can become rough and crumbly, or can separate from the nail bed. Topical and oral antifungals are needed which are available under prescription. My sincere advice would be to consult a dermatologist and get a KOH examination of the nail and skin specimen done to confirm the diagnosis.