Good question. I sometimes struggle with this too. iIve confessed some sins several times because I just couldn’t forgive myself. Then a priest told me a very important thing: that I have to trust God who has forgiven me. Not doing that is pride which demonstrates doubt in God’s love and forgivness. It’s difficult and I still struggle with feelings of shame and regret on certain issue but I pray for humility and to fully accept God’s forgivness.