Thank you everyone for your replies and good wishes - I really appreciate it.
I'm just so frustrated and low about all this. I was diagnosed with IC/PBS a couple of years ago and had a cystoscopy. Bladder looked normal. I was despondent because the urologist/my GP could offer no explanation as to why this had happened, nor any treatment other than 'papering over the cracks'. I wanted to know what the cause was and hence a 'cure' if possible. I eventually discovered there is a school of thought which says IC is caused by chronic infection, which made sense to me because my issues had started following what seemed to be a bad UTI. I took antibiotics long-term, high-dose, for around 18 months but was unsure whether this had any beneficial effect. I don't discount the infection explanation - maybe the most likely explanation, for me at least, is that it isn't down to one cause.
I also found out that menopause can cause urinary and bladder symptoms and read reports on menopause websites and forums, written by women who seemed to be suffering exactly the same symptoms as me. My symptoms started when I was aged 54 and perimenopausal, so I decided to try the hormonal approach, hence going to see the gynae in Spring this year, which brings me to where I am now. I suppose I'm really hoping that the addition of systemic HRT will help, even though the Vagifem hasn't, at least not with my main issue, which is the burning.
I avoid foods/drink likely to cause bladder irritation, although don't actually think that what I eat or drink affects my symptoms - I know that it does, for a lot of people. I tried Estring but ended up with an acute UTI, so had to give up on it and am reluctant to try it again. I do use bicarb but am a bit worried about having to use it all the time.
Julation - thank you for the info about Elavil and I'm glad it's helping you so much. It's known as amitriptyline in the UK and I've considered asking my GP for it but had bad experiences with the side effects of this type of antidepressant in the past (was prescribed tricyclics decades ago, for PND) so have been scared to use it. I know that the dose for nerve pain is much lower than prescribed for depression, so perhaps I just need to give it a go.
Does anyone think there is still a chance that the systemic HRT might be the 'magic bullet' I'm looking for, though?!