Have you ever tried hypnotherapy before? I was having horrible flashbacks all the time for years and after doing sessions for about 6 weeks they completely stopped. I don't know if it works for everyone but it really did wonders for me. I'd talk with your therapist about it and see if they can recommend anyone for you to see. I did it about 6 years ago and haven't had any since and now I'm doing cognitive behavioral therapy to help with my other issues. I still get triggered and have anxiety and such but no flashbacks.