You can substitute other antihistaminergics, because that is what helps with sleep. And yes like others said it is true that this is mostly effective at low dosages, at higher dosages it also starts working harder in other ways that can counter your sleep.
I took it for about a year but eventually quit since it only helped moderately with eating and not much at all with sleep (even though I took low doses), and the akathisia at some point just got to be too much.
I think trazodone would be an example of another drug with antihistamine effect. However it also is primarily an anti-depressant. If it is just for sleep you might want to select a different one that is just mostly an antihistamine and not much else. Much cleaner / more selective!
https://en.wikipedia.org/wiki/Antihistamine#H1-antihistamines
After trying a much lower dose of mirtazapine that is of course - and taper for a less rough transition.
(Problem is though: most of these H1 antihistamines are basically all dirty broad-spectrum drugs in one way or another... idk which one is cleanest)