If you want to become happy, if you want to enjoy life... just always move forward. Never look backward, never look back at your past. Don't bring the past in the future. Just simply live with the moment and always enjoy every second that you are living.
Try to improve and never let past hinders your improvement. If you suck in the past and you didn't do well in life.. it is time to change your life and hope for the best. Just simply give your best and that's it. No more analyzing, no more worrying, no more regrets... just one step at a time and you will be fine.
If you've done bad things in the past, if you made such bad decisions then totally forget those things and keep moving forward. Your motion should be always forward, no undoing, no correcting of the past. Just simply live your life, never turn your head back, just focus on what is in front of you and simply enjoy the process.
Because if you will keep on thinking about past then you will just become depressed, you will be stuck in a mud forever. You will become unhealthy, you will not move, in other words... you will become a bum.
Stop making dramas because none of those shits will give you a good life. So what if they treated you bad, so what if they treated you unfairly, so what if you're not blessed? Don't think that way because it will not help your situation, you will become worse if you will think negatively.
You still have a lot of time, you can become very happy if you will just do the right things in life.
So step your one foot forward and enjoy your journey, keep stepping and stepping, there are lot of things to be excited about. There millions of positive things where you can place your focus. Always remember that your direction is only forward, not sideways, not backward.