I had radiation therapy for rectal cancer. Radiation is cumulative so at first, it's nothing. You lay on the table for 90 seconds and your done. I had a total of 28 treatments over 6 weeks. I started to feel the fatigue about 3 weeks in. I had some redness where I the radiation was being focused as well as hair loss in that area. My doctor was able to provide me creams for the redness that helped a lot. I had some GI symptoms but I think it was related to where I was being targeted. Most of the women I saw there for radiation for breast cancer, seemed to have few side effects and were working and being active through the treatment.
Good luck to you. I kept a count down to get through it. It helped a lot. Also know, if you need a break because you are just too tired or sick, tell your doctor. They can give you a little break. You can do it!