It would be great for you to continue walking through the radiation,exercise is encouraged and actually helps to lessen the fatigue, however it you do become tired make sure you do take some time to rest, go to bed little earlier for example. As for the bra situation, I'm not sure how to help with the size difference sorry, for rubbing I'd suggest sticking to non underwire bras, pure cotton, avoid wool, a silk hanky is always a good option, when you get the skin reaction mepilex lite dressings are great to reduce friction.