I have ibs and these symptoms: diahreea, pain in belly, pain in colon, itchy bottom.did a colonoscopy more than a year ago, should i have another one?

Rome 3 criteria: Ibs is associated w/ abdominal discomfort, altered /alternating stool pattern, accompanying nausea, bloating, gasiness. Often improved by stooling, ibs is defined by changes in perception of gut distension, motility, sensation. Diet & emotional stress may be a factor. 1st rule out inflammation, ischemia, infection (as with colonoscopy), then ibs is diagnosed with "certainty" unless risks change.