To Stop Being So Negative

I seem to be addicted to negativity. Whenever I seem to be making progress as getting rid of my negativity, I then seem to sabotage the effort and slide back to where I was. Consequently, I've hurt friends and destroyed friendships I wanted to keep. I so want to break out of this but I'm at a loss as to what to do and how to start. I don't want to end my life as a lonely cranky old crone who no one wants to be around or be friends with! I'm desperate to change this. I need more specific advice than just being told to "stop being so negative." People have said that to me and I always want to cry, "Don't you think I would if I could? But I don't know how!" I so want someone to say they understand where I'm coming from, but it seems all I get is criticism and people yelling at me and hating me. Then I end up hating myself. I will be so appreciative and grateful of any ideas anyone can give me. Am I the only one like this? Am I doomed to be like this forever? If so, I will just check out of this life now, rather than stay around, poisoning everyone and everything. Thank you. BTW, I live in southeast Michigan, USA.