Keep in mind that Heavenly Father wants us to feel peace. Do you think He would be as hard on you as you are on yourself? No, because He is infinitely compassionate. I suspect that you also feel compassion for others. Try having compassion for yourself and allow yourself to let go of self-defeating thoughts. Draw on your relationship with Christ and the power of His atonement to help you with this. And, if you feel very stuck, seek additional help or counseling.
Also, recognize that the small things matter - each minute spent practicing or doing homework or reading scriptures or exercising is growth and it all adds up. President Monson was known for saying "Life by the yard is hard; by the inch, it's a cinch." I tell myself that all the time. The inches matter. -Emilee Knell