I feel like a demon is inside of me. What is wrong with me?

U need to see a psyc. For evaluation and treatment.
Get help. please get help immediately. if you have a PCP make an appointment. if you don't have a doctor then find a psychiatrist asap. if you feel unsafe in any way then please call 911 or present to an emergency room. a therapist might be good too: http://www.goodtherapy.org/find-psychiatrists.html#