Have you ever tried a meditation CD? I used to do that alot and have done some of the techniques when I'm really stressed. Get one with a voice to walk you through it. (The ones with just music allowed my brain to wander too much.) I'll see if I can find mine and get you the name for one. I put the CD in my CD player, put the earphones in and lay down. 9 times out of 10 I would fall asleep to it and wake up some time later, take the earphones out and fall right back to sleep. It really helped me!
Another trick is to put a rubberband on your wrist. Whenever you start thinking negative, give it a little snap. I know that sounds coo-coo, but it does help to physically remind yourself to stop the negative thinking. My mantra was always "that's not my story". Meaning that's not my story anymore. I'm not living my life based on my past.
(((HUGS)))