I Am Undergoing Radiation Therapy, Since The 2nd Week Of

I am undergoing radiation therapy, since the 2nd week of this I have had chronic constipation, none of the OTC remedies seem to help (they all do work - they produce the symptoms of a bowel movement but I am unable to have one). I must resort to harsh 'clear out' products and/or enemas. My oncologist has no solutions, I went to a gastroenterologist who prescribed Lactolosa (not sure if that is spelled right) this was the worst - it gave me tremendous gas and they sent me home when I went for the radiation therapy - they said my intestines were too distended to perform the radiation. I don't know what to do.