Lots of pain in the descending colon, splenic flexure, and sigmoid flexure. bouts of diarrhoea, gas, it's been happening for 9 months now? cancer?

No : Twenties female w. 9 months crampy abdominal pain and gas unlikely to have cancer. She is candidate for diagnosis irritable bowel syndrome (ibs). In that imaging studies have been performed and apparently negative, she should have a consult with a gastoenterologist and obtain a trial of one of the medications helpful to control the symptoms of ibs. Medication side effects or lactose deficient?

Unlikely: Cancer is unlikely to be the cause in a 24 year old. You should go see your family doctor or internist who can give you medication. If it doe snot settle down a colonoscopy may be indicated to check for any internal abnormaliity.