Lamictal helps a lot. I can remember back to 3 years old and I flash constantly especially when I haven't gotten enough sleep. Everything I watch, everything I read... it all sets off memories constantly. I tried to respond with positive alternatives but I find it's actually better to not give the thoughts that time. I started pushing dreams out of my head as soon as I wake up so I don't remember the ones that make me feel bad. When my brain tries to think back at them I immediately send it on to something else like my routine of getting up or sometimes I can just blank it. I've started applying that same tactic to the flashes but it's a little harder since they are solidly in memory unlike dreams that do not go in to longterm memory if you don't think about them.
My greatest point is my persistence.