A think that i can't remove and my mind remember it continuously forcefully even i want to remove it. how to remove this think. it make me unhappy.

Practice Mindfulness: This is a technique to bring your mind to the present moment. It means to 'pay attention' to the present. Most of time our minds dwell on the past or worry about the future. But it is the present that matters most....It requires practice by reading and learning about mindfulness(meditation). Some of the simple techniques are to focus on your breath or practice repeating a mantra.

Obsessive thought?: It sounds like you might be either having an obsessive thought, or re-experiencing a trauma. These situations can be helped a lot with cognitive behavioral therapy and/or emdr -- but you need an evaluation first so that the best help can be given. Fluoxetine by itself is not likely to completely eliminate these experiences, but working with a psychologist/other therapist may provide relief.