So, two years since I started this thread... a lot of water under the bridge.
After *fixing* my back up, I've irritated it again.

Interestingly, however, the second time round confirms some things about the first time, which might be worth recounting. Here's a potted history....
First time around, i developed painful sciatica coming back to riding after broken arms, and couldn't sit down or bend much for ~6 months (flights to the US during that time were
hell!).
CT scan revealed a bulging disc at L5S1 - but this was probably not the *cause* according to back specialist.
Cortisone injection calmed thigns down slowly. Followed by lots and lots of physio and pilates and swimming.
Jan 2012 back on the bike, but finishing Phd meant not too much riding.
From June 2012, probably averaged about 50km a week, though it was lumpy - wife had baby in September.
Lifting baby, plus mucking around with bike position, aggravated sciatica again around this Christmas. Pretty p*ssed to be off the bike
again.
Findings: Working with physio, confirmed a few things. The sciatic pain is most likely caused by the piriformis muscle getting overworked and rubbing up against the sciatic nerve. Ie. 'piriformis syndrome'. careful dry needling brings some relief. Why overworked? Well, it turns out one leg is about 15mm shorter than the other. How could I have gone 30 years without noticing this? In fact, x ray shows my whole right hip is a different (smaller) size to my left one.
Planning to go see Steve Hogg to see what he can do for that one. Also, got a few tests waiting on - like rheumatoid arthritus and some others to rule out other complications...