[IANAD] what you describe might as well be SIBO (as far as i understand in my limited non-professional understanding the bacterial overgrowth can cause the IBS symptoms too though fortunately i was spared that). It took some years in my case to stumble upon definitive test - the lactose based breath test - with all these years doctors dismissing it as "just take the antacid" (which is actually no-no for SIBO), and even with the definitive diagnosis confirmed by the test it is still a struggle to get a right doctor to correctly treat it.