Tailbone: Keeping on with lower back, esp. tailbone (coccyx / SI / sacroileac joint (IS / ileosacral) / sacrum) pain: This is a really old one of mine, many decades before fibro. Got some of it sorted out, but by far not enough, and I'll expand "a bit", cos it's something I'm trying to pinpoint at the moment.
This is maddening: Sitting, too hard or too soft, can cause the worst & most horrible pain, can make me scream inside, cry, feel like wanting burn it out with iron rods, feel like running away from myself... (that'd be an 8 on my scale, my wife says for others that's 12). So fitting to the thread title "Am I going mad?" this can occasionally be one of the most maddening parts of my body problems, so I prefer alternatives to sitting.
Spine diagnoses: A diagnosis early on was sacrum arcuatum or acutum, i.e. the tailbone curves outside steeply, and back in, meaning direct contact to anything I'm sitting on. (This seems to be a typically German way of emphasizing a certain variant of a more bent sacrum, so there is not really an English equivalent but it helps me understand what might be causing the problems. A comment on proz.com says this, and uses the translations "increased sacral curvature" and "angulation").
The other early diagnoses were Scheuermann/kyphosis, 3 slight scolioses and lumbar hyperlordosis.
Recent orthopedist didn't mention all this, thought there is nothing much to explain my pain - a bit of osteochondrosis in the lower back and in my neck, pelvic tilt, 'polyarthralgia' (that was a month before/aside from the fibro diagnosis). Maddening too. Whilst the PTs think there is a lot to explain it and can help bit by bit, but still lots to do.
Back exercises are what I've always had to mobilize it with, 8'/d without fail, so best every morning before doing anything else in case I forget, because even compensation later means a few hours of additional pain, anything the next day means at least 24h of additional pain.
(Generally I need I also need shoes without any heels and a hard mattress, but since fibro with a soft topper and a lambskin under my thighs/tailbone.)
Acupuncture didn't help me, it harmed, very strangely.
Osteopathy did, incl. very direct manipulation, incl. once inside, to flex everything again...,
acupressure similarly, but in a different way.
Twist-stretching everywhere, standing & lying down. Means standing (or lying face down) with feet turned outwards, if necessary very sharply outwards, maybe one in front of the other, alternately, then stretching back backwards and if it doesn't irritate anyone arms up with palms twisted outwards too, then everything inwards, then outwards, each for 10-20''. That also helps against a hard to grasp irritating "lower back unrest" which got worse when I tried levodopa/L-dopa, an RLS-med, but I'll be trying it again some time soon, just to be sure. Getting up and moving a while or cold showering are what I can do to get it down: Cold showering disturbs my sleep less, interestingly, except after 5am.
Back "(hatha) yoga", for upper, middle, and lower back, is something I've had to add to my back exercises since fibro. I use 20 of the exercises that help me most from a DVD, of which I've type them into my mobile to use whenever I need it.
Specific exercises like my PTs show me, or Bob & Brad (PTs, not docs, btw, despite the ties ;-D) and the German 'Liebscher & Bracht' on youtube can help, as @Jemima's recommended. Actually if I have a certain problem and nothing is helping I just type the symptom into youtube and work thru all the videos that might fit. In this case the body part words I've used in the first line above.
Sitting: I tried and still am trying many ways of sitting, e.g. once had a hole cut in a plastic chair, I always need chairs with a hole in the back, anything reclining, like car seats or a soft couch are OK for 10', then dreadful. Car seats I have to put up as straight as possible or sit turned somehow. "Donut" cushions somehow don't work well, nor does sitting on only one side at a time, and things that help others without tailbone problems with their lower backs like balans chairs, wedges, office chairs or gym balls (Swiss balls etc.)
I often have to sit with one foot alternately under my backside. But that's got worse since fibro due to more pain, and the stiffness.
But actually standing and moving a bit was good, so my 'workstation' was an adjustable & swiveable bar stool and table. Then fibro made standing longer than 3' almost impossible, got better, esp. in the last months due to acupressure & GABA.
Best now for sitting is often strangely sitting on the carpet, even leaned against the couch, altho that shd be too hard... or twisted around towards the couch or a stool with my laptop on it.
Lying down: In the first year of my fibro full flare I spent most resting time at daytime on my couch (with laptop). Lying in bed: I'm often twisted on my front, similar to 'recovery position', but twisted a bit more by putting the upper leg backwards. Neck since fibro made that harder, so wedge a pillow or cushion under my head, so it's fairly straight. Now with a lambskin under thighs and partly tailbone I can lie on my back for about 15 mins. (but with a small cushion under my hunchback, so neck and shoulders can fall back, that may also take some pressure off my tailbone.) I've always had to move around changing positions a lot at night. Now with fibro it's got so bad it means having to sleep alone, no fogging over any more or it builds up inside of an hour at the most, which means I have to get up and move for a longer time.
I'm still looking for better sitting possibilities. Often have to take a thin cushion with me to places like outdoor eating, or just not sit.
Our kitchen chair is one of the worst, and I can't find out why. It's hard, with a bit of padding. Neither a thicker nor a thinner cushion is helping, even if I let my tailbone stick out behind it.
What I'm trying now is my bar stool, which is similarly hard plus padded, but at least movable.
In the past I'd often thought hard surfaces are better than soft ones, but I've realized now fibro is forcing me to look more closely that it's only better for the tailbone, worse for I think the buttocks - not sure how that works at all.
Funniest experience was in the rheum./fibro clinic a talk about pain management, where everyone had to sit on terrible chairs, and suffered terribly. I cdnt more than 4', I was leaning against the wall most of the time, like I often do in talks, I always go to the back, so I can stand up, do exercises, and dance a bit if fitting/possible without distracting, or at least move my pelvis in the form of a lying eight.
Cycling is one of the things I thought I could do best, but it's just OK for the first minutes, and I'm a bit distracted for a time, but the saddle for my backside and back is a big problem, so I often used to cycle standing up in between, which fibro has made very difficult. (Also realized that almost everything hurts (feet, hands, elbows, neck) during it and for a while after, but it's still better than walking, cars etc. Knees and hunchback only don't hurt, because I have a high saddle and the handlebar pretty far away, so I'm stretched.)
But I'll be working on changing all seat forms to those that work best ... once I've figured that out...
BTW - despite getting funny looks from orthopedists, I do not have generalized hyperalgesia: When I stub my toe (like just now) it doesn't hurt much (unless it's really bad), if I get a bruise or scrape I usually don't even know where from, etc.