a shaman focuses his/her method on spiritual ways to heal someone. while a witch doctor tends to combine it with many things like herbs, traditional cures, hypnosis, and some medical treatment too. but in modern days, people who are called/call themselves shamans or witch doctors prefer to build their own images. in the place I live, people like them are called paranormals. some are liars. some are honest people.
witch actually is not always related to supernatural thing. in ancient centuries, people called witches were usually alchemists, herb makers, farmers, bachelors, who lived in villages. they had spiritual beliefs too but its just they were not like in stories of witches like people usually hear (who cast spells to hurt people and eat children). most of them were just decent people like us.