morning ladies, sorry I've been off radar having tripped in the garden and giving myself concussion! All good now though.
I'm no expert, but histamine production is affected by estrogen (which is why I also had problems at puberty). When I first started on HRT I was so relieved that so many symptoms were alleviated that I didn't pay so much attention to what else was happening - I only had the realisation that histamine was affecting me again once I'd got everything else under control.
I was taking 2 piriton every night - my GP wasn't thrilled, but said that if I really needed them she was happy for me to continue. However, now I've moderated my diet I've been able to come off them. I've been waking early (around 5 -6 am), but alert and ready to face the world (previously my husband was literally having to drag me out of bed at 0830). I use the time to meditate, do my duolingo, exercise, see the sun rise, etc.. I'm starting to feel like one of those productivity gurus who say you can conquer the world by getting a headstart on your day!!
I remember all too well how awful it is to wake at 4 when you know you're going to be shattered by the time morning comes. For me, my anxiety was terrible at the time, and I think it was a cortisol rush (or something like that) that had me awake despite being exhausted. If I could, I would play a yoga nidra on my phone so even if I didn't fall asleep again I would feel I was getting rest (rather than lie there thinking about how much I wanted to rest). The app 'insight timer' has some free sleep nidras, but there are lots of other resources online. CBT also helped me - I think there is even now a very effective CBT tool specifically for insomnia - if your GP hasn't mentioned it, maybe take a look online. I also found Tapping really helped me calm my anxiety, maybe that would help you too? Again, there is free stuff online (maybe also check out the proper name for it , EFT, Emotional Freedom Technique).
I'm so sorry that you're suffering like this, but I'm starting to come out the other side, and it's amazing to feel well and normal.