I always felt like I’m borderline OCD, though I’m much better now than I used to be. I guess it’s probably more accurate to say I’m anal than OCD, though! :o
It isn’t an easy cross to carry. Do you have a regular spiritual director? I highly recommend it. Say a prayer asking God to send you a good spiritual director. The benefit of having a regular spiritual director is that he will come to know you and your struggles and will be able to guide you much better than simply going to Confession with a priest who doesn’t necessarily know you very well.
And once you have a good spiritual director, listen to him! A good spiritual director will be able to see things going on within us that we cannot because we are too close to the situation.
So long as we do not intentionally leave out a mortal sin from Confession, we are still forgiven of that sin in Confession, even if we forgot to mention it. I also have heard many recommend bringing these sins up at your next Confession if you remember it afterwards, but I see nothing in the Catechism or Canon Law that necessitates this.
Remember, too, that it is not strictly necessary to confess venial sins during Confession. Only mortal sins.
I think it is good advice for those who struggle with scrupulosity to try to “let go” of those past sins and trust that they are forgiven by making a concerted effort not to mention those past sins at Confession (so long as you have been to Confession after committing the sin and did not intentionally leave it out). It’s not easy to do, but with time, it gets easier.
Again, I can’t recommend enough the value of a good spiritual director. You are in my prayers!