It’s important to be realistic about therapy. You may be minimizing the progress you’ve made. As you noted, this is the first therapist with whom you’ve been open. The fact that you finally found a therapist that you are only now beginning to trust should be considered a major accomplishment.
Also, you have only had five sessions thus far. You and your therapist are still effectively strangers. You also have yet to fully detail the abuse that you have endured. Recounting problems and abuse is painful but necessary in the healing process. This is especially true in the beginning of therapy because early sessions often include recounting the most painful aspects of a person’s life.
You said that you felt “a little better” after each session. That good feeling is short-lived but the fact that you show improvement after each session is a good sign. If you continue with therapy, the likely outcome is that you will come to feel much better, and not just for short periods of time.
You asked whether it is normal to find it difficult to fully implement the advice of your therapist (i.e. “he’s telling me how to change my thoughts but I swear my brain refuses to listen to him.”). Yes, that is completely normal. If change were easy, then it would only take a few sessions to cure most psychological problems but that’s not the case. It is impossible to overcome years of severe abuse in only a month. It takes time but it’s worth it. It will be a cure, not just a temporary fix.
To deal with the flashbacks and nightmares, you may want to consider seeing a psychiatrist in addition to your therapist. A psychiatrist would evaluate whether or not you are a good candidate for medication. A reduction in flashbacks and nightmares would ultimately serve to improve the therapeutic process.
No, you are not wasting your therapist’s time nor are you wasting your time. In my estimation, you’ve already made progress. To quit therapy now would be a mistake. I would strongly recommend that you continue with therapy and try to be as open and as honest as possible. The more you reveal to your therapist the better able he will be to assist you.
In your next session, I would encourage you to discuss these concerns with your therapist. It will allow your therapist to explain what you can expect with regard to therapy. Please take care.