Don't allow yourself to fall into the trap of constantly focusing on and analyzing the past. Look back for the lessons, but not to the degree that discouragement takes over. Like you, I get frustrated at the disappointing decisions I've made over the years, especially my younger years. However, I believe that the Savior is much more concerned with us learning lessons and moving forward with optimism than He is with us making sure we've reviewed and analyzed every former mistake to the degree that we become paralyzed with depression, shame, and guilt. He understands why you did the things you did, He understands why you may still do some of the disappointing things you do, and He still adores you and declares that you can change and become what you hope to become. He knows your heart. He knows your desires. Each successful day and each disappointing day can be steps forward if you never stop looking to Him for His mercy, His enabling power, and His direction.