You can try the Fibonacci sequence instead, it's what I use during stressful moments in the daytime. I also focus on how the bed feels, since this draws attention away from the mentality of getting to sleep as a goal (which is counterproductive for the same reason that forcing yourself not to think about something doesn't work).
I hope this post doesn't sound patronizing as that is not my intention at all. I can definitely relate to the frustration you've described, but for other issues. Based on my own anecdotal experience, it's quite unlikely that you've exhausted all the possible solutions. At the very least, you don't have much to lose in trying one new thing.
I found a surprising source of motivation in books about the Eastern Front of WWII. I figure that if Soviet soldiers managed to survive in those circumstances, I can stay calm and collected in much more favorable conditions.