Badders so sorry you are suffering so much.
I have recently been diagnosed with Autonomic Dysfunction with POTs and have an erratic heartbeat as a result. Currently awaiting a cardio appointment, but the consultant I saw feels standard Cardiology are unlikely to get to the bottom of things, as the erratic heart issues are almost definitely autonomic in origin. This was backed up by having one ECG with two abnormalities (one of which panicked my GP) and one totally normal one within one week. Apparently he sees it all the time.
Autonomic dysfunction can cause a ridiculously wide range of odd symptoms. Digestive issues are extremely common, migraines, problems with controlling your temperature (including chills and sweats), neuralgia type pain (in my case stinging/burning skin, allodynia - hypersensitivity/pain) flushing/rashes/hives, palpitations, brain fog, exhaustion, dizziness, fainting, tremor/tremulousness. I also have problems with excessive (to the point of distressing) yawning episodes, excessing eye watering, facial numbness and more - the list goes on and on and is rarely the same for two people.
A lot of my symptoms are exacerbated by my hormonal cycle and some are at their absolute worst 7-10 days before my period.
A bad episode can precipitate prolonged periods of generalised exhaustion with muscle and joint pain.
My POTs symptoms are pretty consistent, but I also get episodes of tachycardia/erratic heartbeat for no apparent reason - last night one kicked off when I was just lying on the sofa.
I spent years being sent back to Neurology repeatedly, on the assumption that the worst of my symptoms must be neurological in origin, but they were looking at the wrong nervous system, as it's my sympathetic and para-sympathetic nervous systems that are malfunctioning, rather than my brain. Basically, everything that's supposed to run in the background is affected.
I had to go private in the end (dh has a new job that comes with private healthcare) after years of being fobbed off by various doctors in the NHS. The consultant I saw is an advisor to the POTs UK charity, but is actually a General Medicine Consultant and I honestly think general medicine is the way forward for people with a wide range of unusual symptoms that can't be explained by any one discipline. He took a full medical history from birth and spent an hour talking through my specific symptoms, as well as how I feel generally/day-to-day with me, before doing an active stand test and ECG and ordering a tilt-table test, but he pretty much knew exactly what the problem was by halfway through the consultation.
I had never heard of a general medicine consultant until recently - as my Mum was referred to one on the NHS as tests in multiple disciplines had failed to produce an answer for her problems. The GM consultant she saw was able to organise a wide range of tests across different disciplines to get a more complete picture of her overall health, which helped him come up with some idea of where the problem might be and refer to someone relevant to that area for further investigation/treatment.
I wonder if you could ask to be referred to see one via your GP, as their job is to look at the person as a whole, rather than through the blinkered viewpoint of anyone that has a particular specialism.
I'm not saying you have AD or POTs, but ultimately, seeing someone that will take the time to look at you as a whole and join the dots may be the only way to get to the root of your problems.
Also, remember you can ask for a referral to any NHS specialist in the UK, - they may try to dissuade you but you can insist - so perhaps see if you can find out who is the best person to see for Lupus and ask for a referral to them, especially as you were positive on a blood test and the repeated nephritis alone seems to back up that as a probably diagnosis.
Re ablation, I know two people that have had it done and have been really pleased with the results. I'd definitely insist your dh books some time off afterwards though, so that you have time to rest and recover.