I was on another forum today where somebody quoted this:
"during our lives, about 75% of the feedback we receive is negative. Of the 25% feedback that is positive, we receive 80% before we are 4 years old"
I don't know where the figure came from, but it certainly makes you think!
I think it is amazing that you have reached the insight that you have about your situation, and very hopeful. If you can see what the problem is, you have some hope of dealing with it!
Maybe you could look back now, and think about your experience. You said that you had been told all your life that you were no good - I wonder if you can recall when you FIRST became aware that you were receiving that message, and who from? And when you think about the person, or people, who were giving that message to a child, do you have any thoughts about what led them to do that, and whether they understood what the effects might be?