Aw Bev, sounds like you've been doing everything humanly possible to control temperatures - I admit that my suggestions wouldn't really address serious night sweats (of which I've experienced many in previous years, pre-HRT) - perhaps the worst being sopping wet bedding that then goes all clammy and horrible and as you say changing the sheets umpteen times (apart from waking you up even more) only to have them drenched within minutes is one of those things at the top of the 'I can't go on' list.
About all I can think is what helped me, actually got rid of the hot flushes altogether, and that was high strength systemic HRT. In fact I'm just about to start an SSRI AD and I read in the blurb about it that SSRI's can help with hot flushes too. Having said that, if you're on Amitryptaline, I always thought that was supposed to help?
Again I suppose I would urge you to consider upping the oestrogen strength of the HRT you're taking, and live in the expectation that it WILL work, eventually. (And I'm talking weeks, not months, as in my case).
Best wishes to you