Sorry, I didn’t have radiation (mastectomy for me) but less than three weeks doesn’t sound too unusual to me. Bear in mind that sometimes your body and brain have a bit of a well earned slump - after surgery, not just radiation, and the whole emotional impact of the thing, even for those who have got through everything remarkably well. Perhaps try pushing through for just one day next week, and see how it goes. Just some general, round the house activity, perhaps a phone chat to someone, just to feel back in the swing a little bit. Best wishes.