I just finished treatment for breast cancer, including chemo and radiation. I did not have a problem with constipation at all. One reason may be that my diabetic medication (metformin) has a tendency to cause "loose stools" so it may balance out any potential constipation issues. But I do have a couple of thoughts...
First and foremost, hydration is so important. Are you drinking enough fluids? I try to get 96 ounces a day and made sure I got at least that during treatments. It can be any liquids, juicy fruits,
and veggies, popsicles, soups, etc. Any liquid counts and helps.
Next, are you getting enough fiber? Fresh fruits and veggies, nuts, beans, whole grains...it all adds up and contributes to the bulk necessary to keep things moving.
Are you on prescription pain meds? They are notorious for causing constipation. If so, you may just need softeners and laxatives.
There are sugar-free products on the market that contain sugar alcohols (maltitol is the most common). Candies and cookies are popular treats made with maltitol. They cause diarrhea if you eat too much of it. But a small amount might be preferable to taking a pill and be the solution.
And last but not least, to the extent you feel up to it, mild exercise is important. Walking is simple enough and can help you feel better overall.
I hope these ideas help you.
Michelle