I'm just another sufferer like you, not a T or any kind of mental health professional. But I've done what you describe yourself as doing. And I'll tell you what works for me.

Computers keep me awake, so I turn them off early, at nine or ten. Then I lie down and close my eyes and start one of my "sleep fantasies." "Sleep fantasies" are just things that are very peaceful and relaxing to me. Some of them would be quite strange to others but they put me to sleep. You'd have to experiment and see what fantasies you could think up that help you fall asleep.

As for the nightmares, I keep a large pad and pen or pencil on the night table next to the bed. If I have such a dream I wake myself up immediately and write it down. That kind of transfers it away from the worries in my head and makes it much easier to lie down and go back to sleep.

As for thinking about bad things before you go to bed, you just have to refuse to do it. You (and everyone) have control over what goes through your mind. You just have to lie down and tell your unconscious you don't want to think about bad things, just good things. You can do this, really. There are plenty of other times to think over painful or threatening matters. While you're trying to fall asleep is not one of those times.

I also use melatonin and amitriptyline to sleep. And all in all, everything relating to sleep is now, for me, working fine, though I've had life-long sleep problems previously.

Hope you're successful in getting a good night's sleep on a regular basis!