PTSD does that.

The harder you fight anything, the stronger it becomes.
Try planning a different type of day for yourself, if you can. Do something you would normally enjoy, filling your time and also telling your mind that you are safe now. So, maybe take the day off from work? If you can't do that, they plan a special lunch time activity, and a reward for when work in done for the day.
Otherwise, some people find taking the day and burrowing down in bed and nurturing themselves works for them.
I hope that as you plan other things for that day, that the anniversary will become more and more faded.