Here is something worth exploring - it is called "bile acid malabsorption" and the cause can be pelvic radiation AND colon resection. Double whammy here! The medication for this condition is Colesevelam which is a bile acid sequestrant. The blood test for this condition is "bile acid synthesis 7ac4". It will be difficult to find a doctor with access to this test however you could try Colesevelam for a week pre-emptively under your doctor's supervision and see if it helps. This medication does not enter the bloodstream, so there are no conflicts with other meds - it acts like a wick, mopping up the excessive bile acid. Must be taken with food so it has "transportation" through your system and can wick away. I suffered for 7 years with some issues very similar to yours and am now able to manage food without the previous issues. If you decide to try this, pls come back to share and for any questions related to this application. Do google the name of the condition, of the test and of the medication to see if it might work for you.