My husband had the same. Radiation and surgery. He developed crohns most likely from radiation. And pain meds Ocxy, hydromorohone, fentynal patches, etc contributed to this. He started taking Miralax 2x day. Then progressed to senna and a stool softener. Always have suppositories in hand. And eventually palliative care prescribed lachulose which he took only needed and In worked pretty quickly. For gas pains or constipation pain, try put aloe juice. It worked instantly for my husband. He would literally be in toilet yelling in pain. And pure aloe relieves it instantly.