Why not just let go of yesterday, learn from it, so that you’ll be able to have a better tomorrow. If you are ever going to get past having an attitude full of complaining and bitterness you must be willing to work at it daily. You will have to actively take part in doing things to change this damaged mindset like practicing being thankful when you are tempted to just complain.
The best thing to do is let your mistakes go. Focus on the things that are positive that are happening in your life, and be willing to say goodbye to the things in your life that only cause you to complain and wear you down.
Let go of yesterday. Let today be a new beginning and be the best that you can, and you’ll get to where God wants you to be. Make life yours. Get past the mistakes of the past by learning from them and moving on. Change what you can today; make it better today. For this will ensure a better tomorrow.