Is it normal to hear voices in my head?

No: It is best you talk to your doctor. The fact that you are hearing voices, and that it concerns you, makes it not normal. Go to your doctor and discuss it well, and if needed you can be referred to someone who can really help you.

Since the voice is inside your head it may be that you have an active imagination and this is your way of trying to deal with issues. First have a physical examination by a Doctor to know if you have an illness. Please see a Clinical Psychologist with expertise in multiple types of psychotherapy and a Psychiatrist for medication.