From a Christian standpoint, how can you let go of your past and move on?

I've been a Christian for as long as I can remember but strayed away for a while as we sometimes do. I asked God begged God for forgiveness and rededicated my life to him and moved on from my past. I believe that I have been forgiven but my past still haunts me. Nothing too bad just a lot of promiscuity. I want to let go of it but I'm constantly reminded. I think of hoe great God is and how he delivered me but I can't help but to still beat myself up and feel guilty. How can I move on and let it go?