At 19 My Husband Had A Traumatic Appendectomy And Gallbladder

At 19 my husband had a traumatic appendectomy and gallbladder removal in one day. He's 34 now, and has been dealing with IBS ever since. He's had colonoscopy, ultrasound, prescriptions, probiotics, natural remedies, etc. Nothing "fixes" it completely and nothing has made it better for more than 30-60 days. Could it be something else that the GI doctor missed with the tests that have been done so far? He also has a history of skin cancer and respiratory issues.