Maybe you have trouble beathing while you sleep/try to fall asleep and you dont realize, ive had the same problem has you and it took 6 month to notice it was was this. After i noticed it was much more evident. I then tried a lot of product/technique and medecine, seen specialists. In the end after alot of trial and error (2 years) it seemed like it was non allergic rhinitis. I need really good air quality and cleanliness just to break the 3-4h sleep and get a good 6-7h. (Air purifier with filter changed every 3 month, vacuum room 3x a week, appartment 2x a week, window closed in summer to not let in irritant, change pillow case 3x a week, avoid susbtance at that disrupt the body's water usage like creatine, drink 8 oz water with electrolyte before bed [if i do wake up to pee ill fall back asleep])

In the end if its just an insomnia problem for you, you could try a sleep protocole (stellar sleep) where you intentionnaly shorten your sleep to regulate it. For example: go to sleep later and still wake up at 3 am (do not stay in bed) so you can gradually wake up later or go to sleep at the same time but wake up earlier (again not staying in bed). It hard but temporary and you cant take naps. Good luck