What Leads To Darkening Of Toe Nail?

Hi,Doctor Lina I have my problem in my 2 thumb and my other in my toe nail has not too black under my nail and I was consult to a specialist Dr here in Canada she told me no medicine I was so disappointed to heard about no other advice to me . I m always reading in the Internet where can I find a good specialist Doctor to help me about my nail problem where I m going ? Thank you Doctor