A stray has sever dog itch, please help?

am from India.I have a stray dog who comes to eat his dinner and this dog is 2 years old and has a bad itch. The fur is gone and the pink skin is showing. Sometimes little water type of thing is seen on his back. I give him a pinch of Sulfur in his food. The food is beef boiled with porridge and sometimes wheat chapattis. I have mixed Sulfur powder with coconut oil and given him a mage also, but no respite for the small thing. I would like you all to please help me ASAP. People who don't know anything about this thing, please don't waste time in answering this question. Answering this question rightly, will save a dog' s life.