What causes my hallucinations?

I have been diagnosed with bipolar disorder, depression, add, ocd, and tourrettes syndrome. I used to be medicated for bipolar, add, and depression but have been unmediccated for 2 years. I am 18 years old and experience horrifying hallucinations. I see things and hear things that are not there. For example, I hear my name, slurs, rude comments, and random noises that no one else seems to hear and deny saying or making such noises, such as I sometimes hear the person I am talking to call me liar or say other things that they did not say. I see shadows, faces, movement, glints of light, shapes, and horrible grotesque images. The images usually look transparent . The best way I can describe them is being like watermarks on a page. the text on the page is what really is there and the watermark behind it is the hallucination, only it seems to be on top of what my eyes see. These images range from horrible nightmarish monsters, to shadow like people, to people hurting themselves. My most recent was a finger being sliced up repeatedly by a shaving razor. They seem to be brought on by thoughts, the images, and can last and mutate for days. the other hallucinations are more realistic to me and appear to be part of what my eye sees, and I only discover them to be hallucinations when I investigate what I am seeing. What could these be from? I am constantly terrorized by these and would like some answers.