You are the one choosing what thoughts you entertain. You have refused to think positive thoughts because you have put your focus on thinking negative thoughts about yourself – and what you choose often becomes easier and easier to choose again. But it IS a choice and it is ONLY a thought. You CAN CHOOSE A DIFFERENT THOUGHT.
You can begin right now to refuse to think negatively about yourself. Just observe the thoughts you choose for an hour and allow yourself to laugh when you hear yourself criticise yourself – “Aha, I am doing it right now. Good for me that I am finally aware of it. I will choose a more soothing thought right now” – and continue to practice.