That reactive arthritis diagnosis is important - make sure you mention that. ReA can turn into AS, or it could have been misdiagnosed AS in the first place. Whatever, it shows you already have had a spondyloarthritis diagnosed and that should get you somewhere. At the same time you talk about the ReA make sure you also add in that you had had the SI pain before that, but didn't see any docs about it.
IBS - yes, can very easily be written off with that, especially in the NHS and especially in combination with a suggested diagnosis of fibro. One way you could introduce it is by saying "I have GI symptoms of.... but haven't had any kind of testing or investigation for that so far, so I don't know if its just IBS or something else". They actually shouldn't diagnose IBS until they have done some testing to rule out IBD.
