Yes the GAPS diet seems like a good start, at least for me. The theory being that part of why people react to all of these starches is that they have an inadequate ability to break down food in their gut thanks to eating too much junk food. But I don't know if it will work or not, but waking up because of pain in my back is the best motivator I have for changing my diet, that much I do know!
I'll be sure to check out cronometer as a guideline along with my iodine testing.
Do you use black pepper in your diet or not? I don't know if I react to it or not, but it turns black with iodine, so I have removed it for the last few weeks (I do miss it though!!)