I’m lying in bed right now, and am genuinely exhausted
There’s your problem, right there.
Bed is for sleeping and (almost) nothing else.
No reading, watching TV, ipad, eating biscuits, looking at your phone. Nothing.
You need to train your body to make the connection that bed = sleep.
Lying awake in bed worrying about not sleeping strongly reinforces the mental connection that bed = no sleep
If you can’t get to sleep within 15 mins, get up and do something until you feel tired enough to sleep. Read, do the ironing, have a drink , whatever. Even if you’re up for hours, stick with it.
If you feel tired, go to bed and if you can’t sleep within 15 mins, get up again…
I suffered horribly with insomnia for years in my twenties until i started doing this. Now I get into bed, close my eyes and i’m asleep in minutes.