Is your problem likely to be SIBO (small intestine bacterial overgrowth) and not ‘just’ IBS? How do you find out? Well, I came across this free questionnaire today that might help. It leads you to an Australian test site, but you can order the excellent Aero Diagnostics test here if needed. Read about half way down the Overview for more info on it.
Meantime, have a go at the questionnaire:
Hope that helps.