Steve,
You have the right attitude to get through this and I commend you for for your approach of staying with your normal activities. Keep it up, week by week. We all have different experiences with the rads, but most experience some fatigue around the 50% mark. In my case, I kept up good activity until I hit the wall, and did my best to fight through albeit at a reduced level of activity. You are doing great, so stay strong, stay with your program and keep that positive attitude, day by day and week by week.

Bob