Radiation does cause fatigue, and it hangs around for awhile. In my case, after getting through surgery then chemo, it surprised me that it was the radiation that killed my energy. Things slowly but steadily improved over about six months. My doctor warned me about this, and also said that I might not get back to 100%. At the time I felt like I got to 95% and stayed there, which still felt like a great result after eight months of treatment.