Are you a Christian? A Christian cannot be possessed by the devil.
"Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, [SUP]20 [/SUP]for you were bought with a price. So glorify God in your body." 1 Cor. 6:19-20.
The Holy Spirit cannot exist where there are demons and darkness. In fact, when God comes into our hearts and lives, the light of the Holy Spirit chases away such things.
If you are experiencing some kind of problem, you may need to really seek God and get help from your pastor.
In the meantime, I will be praying that God will take what you are experiencing and use it for good. Whatever you are experiencing, just remember that God is always in control and he loves you.
PM me if you want to talk more about what is going on in your life and I can share how God has helped me through some real trials and tribulations.
God bless!