Hi Sparkles74,
Sorry to hear you are suffering.
I had bad acid reflux when I was on HRT including the upper back pain you describe, usually during the night. It pretty much disappeared when I stopped HRT, however I am now careful about what and when I eat, especially in the evening. Personally I think acid reflux and gastro issues are yet another set of menopause symptoms which are caused by fluctuating hormones, so I wouldn't just put it down to HRT. But for me it was definitely worse when on HRT.