I don't have colorectal cancer but ovarian cancer stage 4 that involved my colon and have since had my colon removed. During my first go around of chemo treatments, I was the same with the gagging and vomiting. I couldn't even put a toothbrush in my mouth without gagging/vomiting. I lost 40 lbs all together.
I started getting hydration therapy twice a week and what a difference that made!
No more vomiting and the nausea was soo much improved.
I suspect with an illeostomy Dehydration is an ongoing challenge? I was told it would be without my colon.
Hope this helps.