How do you stop bad memories popping up ?

I have bad memories constantly popping up in my head, I can hear the mean things people said to me and I sometimes even feel like I am reliving these memories. Even things where I was not at fault, or where I accidentally hurt someone.

Now it's not necessarily these things that happened to me that bothers me (I don't wish harm on anyone who has wronged me and I learned my lessons) but that they return randomly and it feels like I cannot "get over them."

I try to distract myself by doing enjoyable things, but these memories come up ESPECIALLY while I am trying to do an enjoyable task.

What am I doing wrong ?