Don't assume the worst, but be prepared for the unknown, just in case. Like Lauri, I too worked full time through rads with no problem at all. I was single with no kids, so I only had to take care of myself...depends on your job, home duties, etc. My skin got pink, no burns, no blisters, no problem. The breast tissue got denser and very tender...even now, 8 years later, it is more tender (a tight hug will cause me discomfort), but the appearance did not change. I do not recall much fatigue, but I did take it easy during those weeks. I had nothing but positive things to say about
the experience (as far as cancer goes!). I had a 7:15 am appointment, went in and out in 15-20 minutes each day, then got to work on time and never missed a beat. The techs were very professional and I always felt treated like a person and not a body part.
As for the gym, I'd suggest asking your doctor first, and if ok, try to work a modified routine during the next few weeks...to stay fit but don't push yourself too hard. Don't forget, your body is still recovering from chemo.