My husband also worked full time until the end of his 3rd week of chemo and rads. Then he hit a wall. Whick is exactly what the Drs. told us. But ... he didn't think it would happen to him. He tried to push himself but just couldn't do it. Keep your nutrition up and keep hydrated I can't stress that enough. That was our downfall through this whole ordeal. He fought the feeding tube so long that he didn't have a choice around wk 4-5. It really helped him alot.
stay strong!