Hm, don't really know what to tell you. I had my natural water birth last time but was in a LOT of pain and pretty traumatised for a long time. I remember going to read my notes at the hospital and being close to tears about half a year later. I've not really thought about it in a long time now though and when I do think about it, I'm at peace with it. I'm not even scared of my upcoming second birth so I guess I must have somehow got over it. Maybe what I'm saying is "time will heal all wounds"?
But then, if it's upsetting you, maybe you need more closure? You can request a "birth debrief" meeting where a midwife or consultant will go through your notes with you. Maybe having a better understanding of why and how things happened will help you put them behind you? Or maybe you could try writing down a detailed account of your memories, including how you feel about what happened and any fears you might have for the future. Or talk it through with your OH or a good friend. Often these things come with feelings of guilt or having failed and often it takes some digging to find out that that's what's wrong. Exploring your feelings about the birth will be a first step to letting them go.