Firstly you have to ask yourself a lot of questions as in are you 'sure' it is a demon, then what are you identifying as a demon. Many things has been called demon in all walks of life and religion. How did you pick up this follower and are you doing anything that could compound the effect it is having on you.
You not walk into your doctors and give him a sketchy outline of your symptoms and expect him to cure you from that.
Your best tool is knowledge, there is a great amount of truth to Know your enemy