20 years ago I developed inflammation of the left sacroiliac joint, after a few years in a manual job (working with horses) which meant endless standing, bending and lifting. It was misdiagnosed for a while, but an osteopath finally pinpointed this joint, I had some brief treatment, gave up the horses for an office job and recovered.
Over the years it has flared up occasionally, and I treat it with ice packs and rest. It rarely lasts long and just a bit tiresome, however...right now I'm stuck in a hotel in Norfolk and in pretty serious pain. 
I think I "tweaked" it last week after some long periods of standing, carrying and bending (running a 2 day conference). I've done 5 hours of driving today and now the pain is going right through me and it hurts even to move slightly.
I doubt my GP can help, presumably it will be written off as generic back pain and they'll offer me ibuprofen. Is there any point trying a chiropractor or osteopath?
Or do I wait it out and let it fade away by itself?