ninjungle - went to the Baby Cafe in Croydon (fantastic organisation, www.thebabycafe.co.uk), where there's a lactation consultant who will see everyone who turns up - unlike the one at Georges who has a 4 week waiting list. Also means you can be there all morning and get help feeding when your baby wants to feed, as opposed to having a set appointment time. And you get tea and biscuits!
She noticed that A really did have thrush but hidden at the back of his mouth, and prescribed Daktarin gel and another 2 weeks of flucanazole for me, plus acidophilous capsules 3x daily, and the sugar-free diet which I'd already returned to, and suggested grapefruit-seed extract, both to drink to lower my pH, and to wash my breasts in.
Managed to get GPs to prescribe the drugs, tracked down the rest at a local health store (not H+B who didn't know diff between grapes and grapefruit...), stocked up on sugar-free chocolate (surprisingly good!), and within two weeks was a LOT better. Now eating a bit of sugar but not much. Any remaining problems are just tingling when A hasn't fed for a while now he feeds less often, and sometimes a dodgy latch on the left as A likes sneakily sliding off it.
Now just need glass in the windows in the loft to stop rain coming in, and I'll be a happy bunny!