I had breast conserving surgery followed by 16 rounds of radiotherapy and walk daily for one hour as well as gentle exercise class twice weekly.
The week after radiotherapy I started exercise class and found myself engulfed with fatigue the first week - needing a lengthynap after class.But thereafter all was fine.
I purchased a Target post op front opening bras for after surgery which I found good during radiotherapy but they did get very discoloured due to all the creaming during/after radiotherapy.I threw them out eventually as a friend bought me my first ah bra which I found great - first I had felt comfortable in months. I still wear them today and are great out walking - no seams to rub and good control.
Ah bra are called sports bras and available many shops and quite cheap.My favourites are from K mart but Best and Less , Target etc all sell them .