In my experience Benadryl has a paradoxical effect after just a few nights...it made me wired...which made me think I needed more...which made me sleep even worse. I stay far away from that now.
Nothing has helped me sleep better than being sober for eleven months combined with regular exercise outdoors. I still have those nights when my brain won't shut off, but I also find that sober I can get by with less sleep with less misery.
Hope you find an answer...it is really miserable.