Maybe you are not tired enough. One advice a professional gave was to not stay in bedroom unless you go to sleep and also no other sofas in the house for too long.
What / how much do you eat / drink in the afternoon and evening?
use melatonin
My understanding (based in part on personal experience) is that melatonin helps mostly with falling asleep, but not necessarily with staying asleep.
What have you tried? We're working on a wearable which measures your sleep state and influences and trains your brain for better sleep performance. Still in development, but check it out https://soundmind.co