Skin discoloration. Of my leg condition.

In the month of November, I got bitten by leeches. After that, I got irritation in my skin where medium sized red bumps were developed all over my legs. I consulted dermatology for the treatment and doctor had prescribed tablet and 1 lotion. With the lotion, because of the way I applied white patches appeared around those red bumps. Again after using one more cream around those places, my skin has become worsen by developing discoloration around the places where I have used the cream. The skin is very dry over there and the color of my skin has turned to black. I am highly worried about this as it really looks weird on my skin. Please help me to know the cause of it and suggest me a very good medicine which can make the skin to my normal color. Please find the attachments, clear picture of my leg condition.