For three or four years my toenails have looked as they do in the photo. They grow up to a certain point seeming healthy, then suddenly the toenail darkens and seems thicker and a new one begins to grow with it. They always grow up to the point in the photo and then the problem returns and a new healthy toenail starts growing, pushing the old one out. My dermatologist put me on anti-fungal medication, when my testing for fungus was positive, but now the tests come up as negative. I've also tried medicated tape and drops for treating psoriasis, but the problem returns. Is there anything else this could be?