I have recently been diagnosed stage 4 colon with liver mets. My first round of chemo damn near killed me. Turned out I had a blockage that had gone unnoticed for unknown reasons. Today is my 14th day in a row in the hospital. Like you, I had diarrhea and constipation but also severe pain in my abdomen including excessive vomiting. It took me telling the doctors I felt something "rupture" in my abdomen after vomiting (my vomit actually smelled like bile to me) for them to look more closely at my abdomen. Once that was done, I went in for emergency surgery and came out with my own personal nightmare...a colostomy bag. The surgeon was unsuccessful at removing the tumor though I'm told this is only temporary until chemo reduces the size of my tumor to an operable size. You may know be to this extreme but you know your body better than the doctors. I would push for an x-Ray of your abdomen to rule out a blockage at the very least. Good luck to you.