IIRC first generation antihistamines are not good for your brain when taken chronically in higher doses, I would definitely look into those effects.

CBN is a federally legal cannabinoid that is reportedly pretty good for sleep, not causing intoxication or interfering with REM like THC does.

I have not tried it, although I do regularly use THC (also not good for the brain) for sleep that, along with a meal, reliably gets me asleep very quickly, although unfortunately without noticeable dreams and with a distinct laziness in the morning, but with these negatives somewhat mitigated when magnesium l-threonate is added.