Have you been tested for sleep disorders?
I know from personal experience that if the brain is afraid that you will, for example, stop breathing in your sleep, it is extremely reluctant to allow you to go to sleep. The mind races, there's always something you can't stop thinking about, and you get less and less sleep at night. It seems like it's made up of many other problems, and you try a million things like meds to get to sleep, but really it is the reptile part of your brain being afraid you will die in your sleep and thus keeping you awake.
If you have insurance, it's worth doing the test to find out for sure. The first pass for most testing is just to tape something to a finger for the night and see what your oxygen saturation levels do overnight in your own home, in most cases. It is easy, then they pick up the device and analyze the data and see if you're oxygen levels are dropping. If so they will order a full sleep study.
This might not be your problem, but it certainly sounds like you've tried most other options and this one, if it is going on, can make gigantic amounts of difference if you get a CPAP machine and mask that really works for you. If it becomes relevant and you don't have very very tiny nostrils, I personally find the nostril masks much easier to sleep with than the other kind which tip and leak into my eye and other such problems more often.