Isaiah43:25 I, even I, am he that blotteth out thy transgressions for mine own sake, and will not remember thy sins
There was a time in my life that I battled with guilt. It weighed me down so much that I couldn't pray, fast, read bible and do other spiritual things. The devil spoke severally to me that God can't forgive me and that I would have to undo ALL my past sins and receive Christ into my heart again even after I became a preacher. I know you've been there before.
When you look at the scripture above properly, you'll discover that God forgives our sins not even because of us but because of him. His eyes cannot behold evil and that is why he is quick to forgive us of our sins provided we ask for forgiveness. The devil preached his gospel to me and I almost swallowed it hook line and sinker. The worst moments of my life was when I began to disregard the efficacy of Christ's blood.
If the devil can steal the initial boldness you had about God's love and how he had forgiven you of your past sins when you accepted Christ, he would keep you in perpetual guilt. When God forgives, he forgets. God is no longer counting men's (including you) sins against them any longer but He is seeking to reconcile us to himself through christ.
The day you understand that Christ's righteousness is now yours, you won't have a problem with guilt one more day.
Father, thank you for forgiving me all my sins, I refuse to sink into guilt one more day In Jesus Name.