I suffer from peripheral neuropathy, as well as other types of neuropathy that are not peripheral. Normally, peripheral refers to the edges, or outer reaches of your nervous system and the smaller branches of nerves. So typically, the pain or abnormal sensation of any kind, like numbness, stinging, tingling, burning, pressure can start in toes, or feet, fingers or hands and creeps upwards slowly as it progresses.
However, you have had it in areas that are not quite typical of peripheral, so perhaps there are some specific nerves that are affected. I know quite a few friends of mine have had entrapment of sciatic nerves, around the sacral/lumbar region (your tail bones) and that squeezing of the nerve has given abnormal sensation in either of their legs, their thighs and their buttocks. Compression of sciatic nerves can be due to a variety of reasons. My OH has it because he has a prolapsed disc in his vertbrae pressing on nerves.
My other friend has had it after a bike accident. And my father had it after having crumbling of bones and in spine and arhtritis, where nerves were trapped.
I have also heard of diabetics suffering from it too.
I should imagine if you put your BD to one side, that a normal diagnosis could possibly be due to your previous break/accident and seems typical of what some of my friends have suffered. And I have heard of that happening years after an accident. My father was in a a car accident when he was about 28 yrs old, but then did not start to get spinal problems related to that accident well into his 40s onwards. I would not assume that a prtevious injury had nothing to do with it. Sometimes with a break you can get a weakness which might pop discs out, and then those can trap nerves,....or you can get narrowing or thickening of the broken vertabrae, which with age start to narrow even more and then start to pinch nerves....or you can get little shards of bone that move about and trap nerves intermittently.
As BD can cause vasculitis in any blood vessel anywhere, then it is also possible for that to cause inflammation of any nerves whether main or peripheral because the nerves have a rich blood supply to make them work.
Sounds like your doc was on the right track of thinking it was sciatic nerves that were involved as that was where your injury occurred.
What you might find is that the odd sensations or the pain comes and goes intermittently.
My Oh finds with his sciatica that it helps if he tries to maintain a good weight and keeps up muscle strength by attending a core exercise class that is specifically for that type of problem. Too much exercise can exacerbate inflammation and pinching, but too little exercise or being overweight can cause it to flare up.