Skin lesion. Increase in size with time?

Undiagnosed round skin lesion on shin for last few years. There was no injury or cut beforehand. It simply appeared as a small brown spot on leg, around 7 years ago. Eventually the skin texture changed, colour darkened, centre appeared burnt (pic attached). Currently the overall diameter is slightly greater than 1 cm. The dark portion is flat and feels harder than normal skin, the boundary can be felt as being separate from the surrounding skin surface. There is no pain or itching. Kindly suggest what it is and does it increase in size with time? Please also suggest possible treatments (if there are any) or at least ways to prevent further lesions. I have referred to 5 dermatologist in the last 6-7 years with no help at all. Nobody had a confirmed diagnosis and nobody's treatment (ointments) worked at all. One prescription (propysalic) probably made it worse by making the skin thinner. Please refer to attached pictures (taken before and after applying a moisturizer)